Carbon nanotube and method for producing the same, electron source and method for producing the same, and display

ABSTRACT

A carbon nanotube has a carbon network film of polycrystalline structure divided into crystal regions along the axis of the tube, and the length along the tube axis of each crystal region preferably ranges from 3 to 6 nm. An electron source includes a carbon nanotube having a cylindrical shape and the end of which on the substrate side is closed and disposed in a fine hole. The end on the substrate side of the tube is firmly adhered to the substrate. The carbon nanotube is produced by a method in which carbon is deposited under the condition that no metal catalyst is present in the fine hole and produced by a method in which after the carbon deposition the end of the carbon deposition film is modified by etching the carbon deposition film using a plasma. Therefore, an electron source excellent in the evenness of field emission characteristics in a field emission region (pixel) in the device plane and driven with low voltage can be provided, and a display operated with ultralow power consumption exhibiting ultrahigh luminance can be provided.

FIELD OF THE INVENTION

[0001] The present invention relates to a carbon nanotube and a methodfor producing same. The invention also relates to an electron source,for use and suitable in field emission displays, using the carbonnanotube in its field emission part and a method for producing same, anda display using such an electron source.

BACKGROUND OF THE INVENTION

[0002] Currently, an electron source that undergoes field emission inresponse to a strong electric field rather than thermionic emission inresponse to large heat energy as in a cathode ray tube has been underactive research from the perspectives of both device and material. Anexample of such a conventional electron source can be found in C. A.Spindt (U.S. Pat. No. 3,665,241), which discloses a pyramid-shaped metalelectron source. As a material of the metal electron source, arefractory metal such as molybdenum is used, for example. The metalelectron source is formed in a hole of about 1 μm. According to theexperiment on field emission characteristics conducted by C. A. Spindt(C. A. Spindt, IEEE TRANSACTIONS ON ELECTRON DEVICES, 38, 2355 (1991)),the molybdenum metal electron source that was formed in a gate openingof about a 1 μm diameter is capable of producing emission currents ofabout 90 μA/tip at a gate voltage of 212 V, which is not low for anoperating voltage. Further, the metal electron source using such arefractory metal (known as a Spindt type metal electron source) has ahigh degree of operating vacuum of 1.33×10⁻⁷ Pa (10⁻⁹ Torr). Inaddition, the metal electron source has weak resistance against ionbombardment and therefore reliability is poor. These drawbacks have beena serious obstacle, preventing the electron source from being put toactual applications.

[0003] Recently discovered by Iijima et al. is a carbon nanotube as aby-product of a fullerene synthesis by carbon arc discharge (S. Iijima,Nature, 354, 56 (1991)). The carbon nanotube, when observed under atransmission electron microscope (TEM), has an encased structure ofgraphite layers that are coiled cylindrically (Y. Saito,Ultramicroscopy, 73, 1(1998)). Such a carbon nanotube is called amulti-walled carbon nanotube.

[0004] As a producing method of another type of carbon nanotube, thereis a technique in which an organic material is applied on a freestandinganodic aluminum oxide film, and then the anodic aluminum oxide film(anodic aluminum oxide layer) is dissolved and removed to separate thecarbon nanotubes, as disclosed in Japanese Publication for UnexaminedPatent Application No. 151207/1996 (Tokukaihei 8-151207). The carbonnanotubes produced by this method have open ends with a diameter of 1 μmor less and a length of about 1 μm to 100 μm.

[0005] There has been active research on electron source using such acarbon nanotube. W. A. de Heer et al. has reported that field emissionoccurs at an electric field intensity of about 10 V/μm with a degree ofvacuum of 1.33×10⁻4 Pa (10⁻6 Torr) and an emission current (voltage: 25V/μm) with a current density of 10 mA/cm² is generated (W. A. de Heer etal., Science, 270, 1179 (1995)). Such a carbon nanotube electron sourceis realized by providing carbon nanotubes on a casting film. The carbonnanotube electron source of this teaching undergoes emission at a degreeof vacuum that is smaller by triple digits or so than the degree ofvacuum required for the metal electron source, and has an emission startvoltage and an operating voltage that are smaller by at least one digitthan those of the metal electron source. These are superiorcharacteristics as the electron source material. Where a carbon nanotubeelectron source that undergoes emission of a large current at a lowvoltage is desired, orientation control of carbon nanotubes becomes animportant technique.

[0006] Orientation control of carbon nanotubes is an important techniqueto obtain a carbon nanotube electron source that undergoes emission of alarge current at a low driving voltage. Japanese Publication forUnexamined Patent Application No. 12124/1998 (Tokukaihei 10-12124)(Japanese Patent No. 3008852) discloses an electron source whereincarbon nanotubes are provided in the pores of the anodic aluminum oxidefilm and a gate electrode is provided at the opening of the pores. Thiscarbon nanotube electron source has carbon nanotubes that grow from ametal catalyst, a growth point, that is embedded in the pores of theanodic aluminum oxide film. This carbon nanotube electron source issuperior in terms of orientation control (order of orientation) of thecarbon nanotubes, and therefore has a promising future. Further, thiscarbon nanotube electron source has improved stability over time ofemission current density. The carbon nanotube electron source also has agreatly improved electron source density that is several thousand timesgreater than that of the conventional Spindt type metal electron source.

[0007] As with the foregoing Tokukaihei 10-12124, D. N. Davydov et al.(D. N. Davydov et al., J. Appl. Phys., 86, 3983 (1999)) disclosesproducing carbon nanotubes whereby growth of carbon nanotubes originatesfrom a metal catalyst that is provided on the bottom of the pores of theanodic aluminum oxide film and thereafter a portion of the anodicaluminum oxide film is removed to obtain carbon nanotubes with exposedtips.

[0008] As schematically shown in FIG. 38 and FIG. 39, the carbonnanotubes that are produced by such a method grow upward from the bottomof the pores of an anodic aluminum oxide film 35 which is provided on analuminum substrate 30. The carbon nanotubes grow into two differentshapes depending on the growth time (extent of growth). That is, whengrowth of the carbon nanotubes is stopped before it reaches a sufficientlevel, carbon nanatubes 38 (oriented carbon nanotubes) that are formedin parallel in the pores of the anodic aluminum oxide film 35 areobtained, as schematically shown in FIG. 38. On the other hand, byallowing sufficient growth, carbon nanatubes 36 (random carbonnanotubes) that are interwound randomly on the anodic aluminum oxidefilm 35 are obtained, as schematically shown in FIG. 39. According tothe study done by D. N. Davydov et al., the emission start electricfield intensities of these two types of carbon nanotubes were different;30 V/μm to 45 V/μm for the oriented carbon nanotubes and 3 V/μm to 4V/μm for the random carbon nanotubes (D. N. Davydov et al., J. Appl.Phys., 86, 3983 (1999)).

[0009] However, the conventional electron source using the carbonnanotubes, while it requires a lower operating voltage (device drivingvoltage: applied voltage at which a practical emission current density(about 10 mA/cm²) is obtained) than the conventional Spindt type metalelectron source, still requires a driving voltage of several hundredvolts, which is still high. This is because the emission start electricfield intensity or operating electric field intensity of theconventional carbon nanotubes (electric field intensity required toobtain a practical emission current density (about 10 mA/cm²)) is notlow enough (e.g., carbon nanotubes formed by a conventional arcdischarge method have an emission start electric field intensity of 10V/μm and an operating electric field intensity of 25 V/μm).Insufficiently low driving voltages have put restrictions on drivers ordevice structures. Thus, there is a need to further reduce emissionstart electric field intensity and operating electric field intensity.

[0010] The present invention was made in view of the foregoing problemand an object of the present invention is to provide carbon nanotubesthat require less emission start electric field intensity and lessoperating electric field intensity, and to provide an electron source,using such carbon nanotubes, that can be driven at a lower voltage. Afurther object of the present invention is to provide a lower powerconsuming display that uses the carbon nanotubes in the electron source.

[0011] In the producing method of a carbon nanotube electron sourceusing a metal catalyst as disclosed in D. N. Davydov et al., varyingmanufacture conditions bring about non-uniformity in the shape of carbonnanotubes. That is, the carbon nanotube electron source produced by thismethod has poor emission uniformity. Such poor emission uniformitybecomes particularly prominent when a large device (e.g., a large screendisplay) is manufactured from the carbon nanotubes produced by thismethod.

[0012] The reason varying manufacture conditions bring about pooremission uniformity is explained below in detail. In the conventionalproducing method of the electron source, carbon nanotubes grow from themetal catalyst. Therefore, depending of the extent of growth, twodifferent shapes of carbon nanotubes; the oriented carbon nanatubes 38as shown in FIG. 38 and the random carbon nanatubes 36 as shown in FIG.39 are produced. Thus, when carbon nanotubes that are formed by theforegoing conventional method are used in an electron source device, forexample, such as a display as exemplified by a FED (field emissiondisplay), there are cases where varying manufacture conditions cause theoriented carbon nanotubes and the random carbon nanotubes to coexist.The emission start electric field intensities of these two differenttypes of carbon nanotubes, 30 V/μm to 45 V/μm for the former and 3 V/μmto 4 V/μm for the latter, are greatly different. The coexistence of theoriented carbon nanotubes and the random carbon nanotubes in theelectron source device has a detrimental effect on uniformity ofemission characteristics and causes various problems such as displayflicker. The cause of this coexistence of the oriented carbon nanotubesand the random carbon nanotubes resides in a growth mechanism of thecarbon nanotubes. Specifically, it is known to be caused by the growthof carbon nanotubes that originate from a transition metal catalyst suchas nickel, iron, and cobalt.

[0013] The producing method of an electron source disclosed inTokukaihei 10-12124 also forms carbon nanotubes using a metal catalyst,and therefore has the same problem as the producing method of D. N.Davydov.

[0014] Another object of the present invention is to provide a producingmethod of an electron source having superior uniformity in emissioncharacteristics within a device plane or an emission area (pixels).

DISCLOSURE OF THE INVENTION

[0015] In order to achieve the foregoing main objects, a carbon nanotubeaccording to the present invention includes at least one layer of acylindrical carbon network film, wherein the carbon network film has apolycrystalline structure which is divided into a plurality of crystalareas in a tube axis (central axis of the tube) direction (firstfeature).

[0016] A carbon network film of conventional carbon nanotubes includesonly sp² bonds (sp²-hybridized carbon-carbon bonds), and is structuredas continuous crystals of a single sheet. Such a carbon network film isalso known as a graphene sheet, which has a two-dimensional networkstructure of a monoatomic layer structured from the six membered ring ofthe carbon.

[0017] In contrast, the carbon network film of the carbon nanotubeaccording to the present invention includes dangling bonds (bonds notforming covalent bonds, i.e., unpaired electrons) or sp³ bonds(sp³-hybridized carbon-carbon bonds) in high density, and therefore thecarbon network film (made up of sp² bonds) has a discontinuous structurewhich is divided into a plurality of crystal areas in the tube axisdirection by the dangling bonds or sp³ bonds. In other words, the carbonnetwork film of the carbon nanotube according to the present inventionhas a polycrystalline structure in which a plurality of separategraphene sheets (monocrystals) are disposed on one cylindrical plane.Note that, it is believed that adjacent graphene sheets, between whichno covalent bonds exist, are held by interactions by the van der Waals'force, that is strong enough to maintain the tube structure.

[0018] Preferably, each crystal area is on the order of nm(particularly, several nm to several tens of nm), and more preferably ina range of 3 nm to 6 nm in the tube axis direction. It is particularlypreferable that a length of each crystal area in the tube axis (centralaxis of the carbon nanotube) direction is not more than the tubediameter (outer diameter of the carbon nanotube; on the order of nm). Bythe length of each crystal area in the tube axis direction much shorterthan the crystal length (equal to the tube length; on the order of nm)in the tube axis direction of each crystal area of conventional carbonnanotubes, it is ensured that carbon nanotubes with a reduced emissionstart electric field intensity and a reduced operating electric fieldintensity can be provided.

[0019] Note that, the carbon nanotube may be a multi-walled carbonnanotube that is made up of multi-walled (two to several tens of walls)carbon network films, or a single-walled carbon nanotube made up of asingle-walled carbon network film. Further, the carbon nanotube may be acylinder with closed ends, or a cylinder with a closed one end and anopened other end, or a cylinder with open ends.

[0020] An electron source according to the present invention includes acarbon nanotube with the foregoing first feature as a field emissionpart, thereby providing a lower voltage drive electron source using thecarbon nanotube.

[0021] Note that, as the terms are used herein, “field emission part”refers to the substance (field emission source) itself that emitselectrons, and “electron source” refers to an element (field emissionelement) produced by supporting the carbon nanotube on a support member.

[0022] A display according to the present invention includes a pluralityof carbon nanotubes with the foregoing first feature as a field emissionpart, and electric field applying means for applying an electric fieldto each carbon nanotube so as to cause each carbon nanotube to emitelectrons. This enables the electron source to be driven at a lowervoltage, thereby providing a lower power consuming display.

[0023] It is preferable that the electric field applying means canindividually control the electric field intensity of each carbonnanotube. This enables display to be carried out using each carbonnanotube as a single pixel.

[0024] The following explains crystallinity of the carbon network filmof the carbon nanotube according to the present invention and size ofthe crystal areas in detail. First, the carbon network film of thecarbon nanotube according to the present invention will be defined andits crystallinity characterized.

[0025] It has been confirmed by the Raman spectrometry that the Ramanspectrum of the carbon nanotube according to the present invention has apeak in a G band (Graphite band; 1580 cm⁻¹) that derives from graphite.The result of Raman spectrum analysis has characterized the carbonnanotube according to the present invention to have a relatively largepeak in a D band (Disorder band; 1360 cm⁻¹) that derives from adisordered crystal structure of the carbon network film (graphitestructure).

[0026] The inventors of the present invention have proven by anexperiment that in a suitable embodiment of the carbon nanotubeaccording to the present invention that a ratio (I₁₃₆₀/I₁₅₈₀) of thepeak intensity (I₁₃₆₀) of the D band to the peak intensity (I₁₅₈₀) ofthe G band is in a range of from 0.5 to 1. This ratio is about 5 timesto 10 times greater than that of a conventional carbon nanotube that isformed by arc discharge, for example.

[0027] Further, although comparisons are not quantitative, the Ramanspectrum of the carbon nanotube according to the present invention has adistinct spectrum in which the peak is broader than that of conventionalcarbon nanotubes and the G band near 1580 cm⁻¹ has shifted to the highfrequency side (1600 cm⁻¹).

[0028] Such a Raman spectrum of the carbon nanotube according to thepresent invention indicates that the carbon nanotube according to thepresent invention has low crystallinity and a polycrystalline carbonnetwork film, i.e., a carbon network film of a structure that is dividedinto large numbers of micro crystal areas.

[0029] Next, in order to explain polycrystallinity of the carbon networkfilm of the carbon nanotube according to the present invention, the sizeof the crystal areas of the carbon network film is defined. A width of adiffraction line obtained by X-ray diffraction (XRD; X-rayDiffractiometry) spectrometry is used to determine a crystallite size.This crystallite size is used to characterize polycrystallinity of thecarbon network film of the carbon nanotube according to the presentinvention.

[0030] In a preferred embodiment of the carbon nanotube according to thepresent invention, the crystallite size (La) in the tube axis direction(direction of film plane) of the carbon network film is in a range offrom 3 nm to 6 nm, which is notably smaller than the crystallite size(on the order of μm) in the tube axis direction of the carbon networkfilm of conventional carbon nanotubes. Further, in a preferredembodiment of the carbon nanotube according to the present invention,the crystallite size (La) in the tube axis direction (direction of filmplane) of the carbon network film is in a range of from 3 nm to 6 nm,which is notably smaller than the crystallite size (several mm toseveral cm) of the bulk graphite.

[0031] Further, Japanese Patent No. 2982819 (WO89/07163) discloses acarbon fibril that is in the form of a fine thread tube with a pluralityof graphite layers (equivalent to the carbon network film of the presentinvention) essentially parallel to the fibril axis, i.e., a plurality ofgraphite layers that are essentially concentric to the fibril axis(circular cylinder axis) as shown in FIG. 2 of this publication, and thelength of the graphite layers along the fibril axis (equivalent to thecrystallite size La in the tube axis direction in the present invention)is two times or greater than the fibril diameter (3.5 nm to 75 nm).Thus, the crystallite size in the fibril axis direction of the carbonfibril is larger by about one digit than that of the carbon nanotube ofthe present invention.

[0032] Further, in a preferred embodiment of the carbon nanotubeaccording to the present invention, the crystallite size Lc in thethickness direction (direction perpendicular to the carbon network film)of the carbon network film as determined from a width of the diffractionline obtained by the X-ray diffraction spectrometry is in a range offrom 1 nm to 3 nm, which is notably smaller than that of the bulkgraphite (having a crystallite side of about several mm to several cm).

[0033] The crystallite size La and Lc characterizes the carbon nanotubeaccording to the present invention that crystallinity is low and thecarbon nanotube has a polycrystalline carbon network film, i.e., acarbon network film that is divided into micro crystal areas on theorder of nm. Thus, it can be said that the carbon nanotube according tothe present invention is a carbon nanotube with a carbon network film ofa polycrystalline graphite structure that is divided at a nano level,i.e., a polycrystalline carbon nanotube.

[0034] Further, the low crystallinity of the carbon nanotube accordingto the present invention can easily be explained in relation to planeintervals (002 diffraction line; d(002)) of the carbon network filmobtained from the X-ray diffraction spectrum.

[0035] The bulk graphite has a laminated structure of network planes ofcondensed benzene rings (graphene sheets), wherein plane A and plane Bare alternately laminated at slightly shifted positions. The distancebetween plane A and plane B of the carbon nanotube according to thepresent invention, i.e., the plane interval (d(002)) of the carbonnetwork film is in a range of from 0.34 nm to 0.4 nm, which is largerthan that of the bulk graphite (d(002)=0.3354 nm). It is thus envisagedthat the carbon nanotube of the present invention has low crystallinity,i.e., a low crystalline graphite structure.

[0036] This result of analysis supporting the low crystallinity does notcontradict to the polycrystalline structure of the carbon network filmof the carbon nanotube of the present invention. The polycrystallinestructure of the carbon network film of the carbon nanotube of thepresent invention can be quantitively explained from the Raman bandintensity ratio of D band to G band (I₁₃₆₀/I₁₆₀₀) of the Ramanspectrometry and from the crystallite size Lc and La. These propertyvalues of the carbon nanotube of the present invention, compared withthe property values of conventional carbon nanotubes, are sufficient toexplain the low crystallinity.

[0037] The carbon nanotube of the present invention having the foregoingstructure cannot be obtained by a method of forming carbon nanotubes athigh temperatures (e.g., several thousand degrees Celsius used to formcarbon nanotubes by conventional arc discharge), or a method in whichcarbon nanotubes are formed inside the pores of a porous material usinga metal catalyst. The carbon nanotube according to the present inventionhaving the foregoing structure was made available for the first time bya producing method of a carbon nanotube according to the presentinvention, in which the carbon nanotube is formed inside the pores of aporous material in the absence of a metal catalyst, at a temperature ofpreferably not less than 600° C., or more preferably in a temperaturerange of 600° C. to 900° C. In the producing method of the carbonnanotube according to the present invention, the crystal areas only growto the diameter of the carbon nanotube.

[0038] A producing method of a carbon nanotube according to the presentinvention includes the step of: depositing carbon inside large numbersof pores of a porous material so as to form a carbon deposition film ofa cylindrical shape, wherein the carbon is deposited (carbon nanotube isformed) in the absence of a metal catalyst in the pores.

[0039] Unlike conventional producing methods, the foregoing method doesnot use a metal catalyst, and therefore can obtain a carbon nanotubewith the polycrystalline (low crystallinity) carbon network film, thatgrows inside the pores by a distinct growth mechanism. Further, becausecarbon is deposited in the absence of a metal catalyst, the methodrequires less cost. Further, a step of providing a catalyst is notrequired, simplifying the producing steps of the carbon nanotube.

[0040] Conventionally preferred methods of producing a carbon nanotubeinclude a method, such as arc discharge, which involves hightemperatures anywhere from one thousand several hundred degrees Celsiusto two-thousand degrees Celsius, and a laser evaporation method or avapor-phase carbon deposition method using a transition metal such asnickel, cobalt, or iron as a catalyst. The carbon nanotubes produced bythese methods had a problem of controlling the shape (diameter, length)of the tubes. The method of the present invention by which the carbonnanotube is produced using a porous material with pores in the absenceof a metal catalyst is the solution to this problem. The producingmethod of the carbon nanotube according to the present invention ishighly effective because it uses a porous material with pores and thuseliminates a metal catalyst and enables the shape of the tube to becontrolled.

[0041] It is preferable that the producing method of the carbon nanotubefurther includes an anodic oxidation step for obtaining the porousmaterial; and a heating step of not less than 600° C. after the anodicoxidation step. Further, it is preferable in the producing method of thecarbon nanotube that the carbon is deposited by vapor-phase carbondeposition in which gaseous hydrocarbon is carbonized by pyrolysis. Inthis way, the carbon nanotube with the carbon network film of apolycrystalline structure can be obtained more reliably. Further, by theheating step of not less than 600° C. after the anodic oxidation step,the anodic aluminum oxide film can undergo a phase transition toγ-alumina (particles that are scattered between carbon nanotubes, to bedescribed later). In the case where carbon is deposited by vapor-phasecarbon deposition in which gaseous hydrocarbon is carbonized bypyrolysis, a temperature of vapor-phase carbon deposition, which variesdepending on the type of hydrocarbon (type of reaction gas), ispreferably in a range of from 600° C. to 900° C., when the gaseoushydrocarbon is a propylene gas.

[0042] Note that, D. N. Davydov et al. carbonizes acetylene at 700° C.using a metal catalyst. This differs from the method of the presentinvention including the anodic oxidation step for obtaining a porousmaterial, followed by carbonization of gaseous hydrocarbon (preferablypropylene) at a temperature of not less than 600° C. (preferably 600° C.to 900° C.) in the absence of a metal catalyst, using the porousmaterial with pores as a template.

[0043] Further, it is preferable in the producing method of the carbonnanotube that the carbon network film is plasma etched so as to modifythe tip of the carbon network film (carbon nanotube). By thus modifyingthe end face of the carbon nanotube making up the field emission area,field emission efficiency can be increased and a carbon nanotube with areduced emission start electric field intensity and with a reducedoperating electric field intensity can be obtained.

[0044] It is preferable that oxygen plasma is used for the etching. Thisenables the tip of the carbon network film (carbon nanotube) to beopened as well as oxidized, thus providing a carbon nanotube with afurther reduced emission start electric field intensity and with afurther reduced operating electric field intensity.

[0045] A producing method of an electron source of the present inventionis based on a method in which a porous material (obtained in a step offorming a porous layer on a predetermined area of the metal wires in apreferred embodiment) is used as a support member for supporting thecarbon nanotube and carbon is deposited inside the pores of the porousmaterial (preferably by a vapor-phase carbon deposition method) to formthe carbon nanotube.

[0046] The electron source with the carbon nanotube provided in thepores of the porous material can also be produced by a method in whichisolated carbon nanotubes are inserted in the pores of the porousmaterial. For example, a freestanding porous layer is preparedbeforehand and carbon nanotubes are formed in the porous layer by thevapor-phase carbon deposition method. Thereafter, the porous layer iscompletely removed to isolate the carbon nanotubes, which are thenplaced in the pores of another porous layer by a method such aselectrophoresis. However, the producing method using such isolatedcarbon nanotubes have a problem of accumulation or sticking, etc., andis not necessarily a more desirable method than the foregoing producingmethod.

[0047] In contrast, in the producing method of the electron source ofthe present invention, a porous material is used as a support member forsupporting the carbon nanotube and carbon is deposited inside the poresof the porous material (preferably by the vapor-phase carbondeposition), so as to form the carbon nanotube.

[0048] That is, the producing method of an electron source of thepresent invention is a method of producing a carbon nanotube whichincludes a carbon nanotube as a field emission part, and a supportmember for supporting the carbon nanotube, and the method includes thesteps of forming the support member from a porous material with largenumbers of pores, and depositing carbon inside the pores in the absenceof a metal catalyst in the pores, so as to form the carbon depositionfilm of a cylindrical shape.

[0049] With this method, the carbon nanotube can have a uniform shape inthe emission area and in the device plane. Specifically, an electronsource with carbon nanotubes having a uniform diameter and a uniformlength can be provided.

[0050] Carbon nanotubes of a conventional electron source have theshapes as illustrated in FIG. 38 and FIG. 39, depending on the growthtime. The shapes shown in FIG. 38 and FIG. 39 are of those carbonnanotubes that grew from a metal catalyst, specifically, such as nickel,iron, and cobalt, as an origin of growth. (D. N. Davydov et al., J.Appl. Phys., 86, 3983 (1999)). The following explains the growthmechanism of such carbon nanotubes. At the early stage of growth, thecarbon nanotubes grow from a metal catalyst as an origin of growth. Inthe example of FIG. 38, the carbon nanotubes grow in a straight line inthe pores. When the carbon nanotubes continue to grow past the pores,the carbon nanotubes above the pores are curled as they grow, as shownin FIG. 39. As explained, the carbon nanotubes that grow in a vaporphase from a metal catalyst as an origin of growth are in a straightshape in the early stage of growth as shown in FIG. 38. The carbonnanotubes, when grow past the pores, become curled as shown in FIG. 39.The carbon nanotubes of the straight line shape as shown in FIG. 38 havean emission start electric field intensity of several tens of V/μm,whereas the carbon nanotubes of the curled shape as shown in FIG. 39have an emission start electric field intensity of several V/μm. Thismay cause large non-uniformity of emission start electric fieldintensity in the emission area or device plane. Thus, in order tocontrol the shape of the carbon nanotubes in the emission area or deviceplane, the process of forming the carbon nanotubes needs to be strictlymanaged.

[0051] Contrary to the conventional method of forming the carbonnanotubes as explained above, the producing method of an electron sourceof the present invention does not cause the growth-time-induced shapenon-uniformity. That is, the producing method of the present inventiondoes not use a metal catalyst and the carbon nanotubes do not grow likethe random carbon nanotubes to extend past the pores, even when thegrowth time is long. Thus, the carbon nanotubes are always formed by thetransfer of the pore shape of the porous material and retain thediameter and length of the pores of the anodic aluminum oxide film.Thus, with the producing method of an electron source of the presentinvention, the carbon nanotubes grow by an entirely different growthmechanism from that of the conventional carbon nanotubes that grow froma metal catalyst as an origin of growth, and there will be nonon-uniformity in shape of the carbon nanotubes caused by non-uniformproducing processes. As a result, it is possible to obtain an electronsource with superior uniformity of emission characteristics in thedevice plane or emission area (pixels).

[0052] Further, in the foregoing producing method, by the distinctcarbon nanotube growth mechanism that does not use a metal catalyst, thecarbon nanotubes adhere to the inner wall and entire bottom of thepores. Thus, when the porous material is a porous layer, provided on asubstrate, with large numbers of through-pores, the carbon nanotubes areformed in a cylindrical shape inside the pores with an closed end on theside of the substrate, and the carbon nanotubes adhere to the surface ofthe substrate on the entire side face on the side of the substrate(carbon network film of the outermost layer). Thus, an electron sourcewith the carbon nanotubes firmly adhering to the support member can beprovided. Further, in the case where the substrate or a conductive layeron the surface of the substrate is used as an electrode for applying anemission electric field, an electron source in which no electricalconnection failure occurs between the carbon nanotubes and the electrodecan be provided. Thus, the electron source, not only when it is simplyused as an electron source device but also when it is installed in otherelectrical devices or optical devices, can provide devices with highlyreliable electrical connections.

[0053] In the producing methods of an electron source as disclosed inTokukaihei 10-12124 and D. N. Davydov, an electrical connection failuremay occur between the carbon nanotubes and the base electrode when themetal catalyst at the bottom of the pores of the porous layer is notprovided properly. That is, in these methods, a metal catalyst isembedded in the pores of the anodic aluminum oxide film that is formedon the base electrode, and the carbon nanotubes grow upward from themetal catalyst that is provided in the pores of the anodic aluminumoxide film. Thus, when the metal catalyst is not embedded to the bottomof the pores of the anodic aluminum oxide film but stops midway insidethe pores (not the bottom of the pores), the carbon nanotubes growupward from a midway position inside the pores. As a result, noelectrical connection can be made between the carbon nanotubes and thebase electrode (cathode electrode), which not only degrades reliabilityof the electron source but lowers production yield.

[0054] Further, the foregoing producing method does not use a metalcatalyst and thus the carbon that was generated by a method such asvapor-phase carbon deposition (pyrolysis) of a hydrocarbon deposits onthe inner wall of the pores of the porous material such as the anodicaluminum oxide film. As a result, an electron source with the carbonnanotubes firmly supported on the support member (porous material) canbe provided.

[0055] On the other hand, in the carbon nanotubes using a metalcatalyst, as disclosed in Tokukaihei 10-12124 and Tokukaihei 11-194134,the carbon nanotubes grow without touching the inner wall of the anodicaluminum oxide film, i.e., regardless of the pore shape of the anodicaluminum oxide film (template). Thus, the carbon nanotubes cannot befirmly adhered to the anodic aluminum oxide film.

[0056] Further, in the method in which the carbon nanotubes grow fromparticles of a metal catalyst as an origin of growth inside the pores ofthe porous layer, in the event where a plurality of grains exist in asingle pore, a plurality of carbon nanotubes are formed in a singlepore, corresponding to the plurality of metal catalyst particles(grains). In contrast, in the producing method of the carbon nanotube ofthe present invention, the carbon nanotubes do not grow from the metalcatalyst particles as an origin of growth but grow along the inner wallof the pores. Thus, a single carbon nanotube is formed per pore of theporous layer, transferring the shape of the inner wall of the pores.

[0057] Further, it is preferable that the step of forming carbonnanotubes with respect to the pores of the porous material in theproducing method of an electron source of the present invention includesthe step of removing the carbon deposition film that was formed on thesurface of the porous material, in addition to the step of depositingcarbon on the porous material (preferably vapor-phase carbon depositionstep).

[0058] The carbon deposition film deposited on the inner wall of theporous material (low crystallinity or polycrystalline carbon networkfilm) is similar in film property to the carbon deposition filmdeposited on the surface of the porous material, and by selectivelyremoving the carbon deposition film on the surface of the porousmaterial, the carbon deposition film deposited on the inner wall of theporous material is maintained. This step determines the basic shape ofthe carbon nanotube of the present invention, and only the carbonnetwork film of the carbon nanotube and the cross section in thevertical direction is exposed in air.

[0059] Such a mode is preferable in the producing method of an electronsource of the present invention. That is, the mode is preferable interms of surface modification of the emission area, making it possibleto selectively carry out surface modification only on the carbon networkfilm of the carbon nanotube and the cross section in the verticaldirection. Specifically, the inventors of the present invention haveproven by experiment that the step of removing the carbon depositionfilm deposited on the surface of the porous material is preferablycarried out by etching (dry etching) using plasma, such as reactive ionetching (RIE; Reactive Ion Etching), because it was most effective toimprove the field emission characteristics.

[0060] That is, it is preferable in the producing method of the presentinvention that the tip of the carbon deposition film (carbon nanotube)be modified by carrying out plasma etching. By thus modifying the endface of the carbon nanotube which becomes the field emission area,emission efficiency can be improved. As a result, an electron sourcewith reduced levels of emission start electric field intensity andoperating electric field intensity can be obtained.

[0061] Further, the step of forming the carbon nanotube with respect tothe pores of the porous material in the producing method of the electronsource of the present invention may further include the step ofpartially removing the porous material, in addition to the step ofdepositing carbon on the porous material and the step of removing thecarbon deposition film.

[0062] Further, a producing method of a carbon nanotube of the presentinvention is adapted to deposit carbon inside the pores of the porousmaterial having large numbers of pores so as to form the carbondeposition film of a cylindrical shape, wherein the tip of the carbondeposition film is modified by etching the carbon deposition film usingplasma.

[0063] In this way, the end face of the carbon nanotube which makes upthe field emission part can be modified, thus providing the carbonnanotube with improved field emission characteristics. The inventors ofthe present invention have confirmed that the composition ratio (O/C) ofoxygen to carbon can be increased to 0.15 or greater by carrying outplasma etching with respect to a carbon nanotube whose composition ratio(O/C) of oxygen to carbon is less than 0.15.

[0064] The composition ratio (O/C) of oxygen to carbon in the fieldemission area of the carbon nanotube obtained by the foregoing producingmethod, which is experimentally decided by the X-ray photoelectronspectrometry (XPS), is generally in a range of from 0.1 to 0.3. Apreferable range of the composition ratio (O/C) of oxygen to carbon isfrom 0.15 to 0.2. A carbon nanotube with a composition ratio (O/C) ofoxygen to carbon 0.15 to 0.2 can emit electrons at a low voltage.

[0065] The carbon nanotube that can emit electrons at a low voltage hasa peak (bond energy near 284.6 eV) that derives from sp²-hybridizedcarbon atoms (C1s). The peak becomes broad when the carbon nanotubes issubjected to plasma etching. Further, by plasma etching, the peak (bondenergy near 286 eV) that derives from the C—O bonds of the carbonnanotube becomes notably high. It is envisaged that such acharacteristic is distinct to the carbon nanotube that can emitelectrons at a low voltage.

[0066] It is preferable in the foregoing producing method that theetching is carried out using oxygen plasma. This enables the tip of thecarbon deposition film (carbon nanotube) to be opened as well asoxidized. Thus, the end face of the carbon nanotube (cross section thatresults from cutting the carbon network film in a directionperpendicular to the film plane) that was made by opening the tipconstitutes the field emission area, and the end face making up thefield emission area includes oxygen rich carbon. As a result, the carbonnanotube with further improved field emission characteristics can beobtained.

[0067] In a producing method of an electron source of the presentinvention, the resulting carbon nanotubes are used as the field emissionpart and the porous material is used as the support member forsupporting the carbon nanotubes. That is, the producing method of theelectron source of the present invention is a method for producing anelectron source which includes a carbon nanotube as the field emissionpart, and a support member for supporting the carbon nanotube, andmethod includes the steps of: forming the support member using a porousmaterial with large numbers of pores; and forming a carbon depositionfilm of a cylindrical shape by depositing carbon in the pores of theporous material, and plasma etching the carbon deposition film so as tomodify a tip of the carbon deposition film.

[0068] By thus modifying the end face of the carbon nanotube whichbecomes the field emission area, emission efficiency can be improved. Asa result, an electron source with reduced levels of emission startelectric field intensity and operating electric field intensity can beobtained.

[0069] An electron source of the present invention includes a pluralityof carbon nanotubes that are disposed parallel to one another as a fieldemission part, and the electron source further includes: particles(preferably γ-alumina grains), dispersed between the carbon nanotubes,that bind side surfaces of the carbon nanotubes adjacent to one another(third feature).

[0070] Tokukaihei 10-12124 and D. N. Davydov et al. disclose electronsources of a structure in which the carbon nanotube is entirely encasedin the pores of the anodic aluminum oxide film (Example 1 of Tokukaihei10-12124), and of a structure in which the tips of the carbon nanotubesextend out of the pores of the anodic aluminum oxide film (extends outof the film plane) (Example 2 of Tokukaihei 10-12124 and D. N. Davydovet al.). These are structures in which all or most of the side wall ofthe carbon nanotubes are covered with the anodic aluminum oxide film.For example, it can be seen from the SEM photograph of the carbonnanotube of D. N. Davydov et al. that a flat surface of anodic aluminumoxide film remains in the structure (D. N. Davydov et al., J. Appl.Phys., 86, 3983 (1999)).

[0071] In a structure like these, the electric field does not easilyconcentrate on the carbon nanotubes, and the electron source having sucha structure has a high operating electric field intensity.

[0072] In contrast, in the electron source having the foregoing thirdfeature, particles are dispersed between the carbon nanotubes. Thus, anarea (tips) of the side wall of the carbon nanotubes except for the areaof the face adhered to the particles is exposed to air. That is, theside wall has a large exposed area. In other words, the carbon nanotubeis sufficiently exposed to air. This enables the electric field toconcentrate on the carbon nanotube, thereby providing the electronsource that can be driven at a low voltage.

[0073] Further, the electron source having the third feature whereby thecarbon nanotubes are anchored via dispersed particles (isolationparticles) can provide a structure that can improve packing density ofthe carbon nanotubes (structure that allows for a large emission currentdensity).

[0074] A display of the present invention includes an electron sourcethat is provided with a plurality of carbon nanotubes having theforegoing structure, and electric field applying means for applying anelectric field to each carbon nanotube so as to cause each carbonnanotube to emit electrons. This enables the electron source to bedriven at a low voltage, thus providing a low power consuming display.

[0075] An electron source of the present invention includes a carbonnanotube as a field emission part, and a support member for supportingthe carbon nanotube, wherein the support member is a porous materialwith large numbers of pores, and the carbon nanotube at least partiallyadheres to the inner wall of the pores (fourth feature).

[0076] This provides a highly reliable electron source with the carbonnanotube firmly supported by the support member.

[0077] The carbon nanotube that adheres to the inner wall of the poreswas produced for the first time by the producing method of the presentinvention by which the pore shape of the porous material is transferredand the carbon nanotube is formed by the growth mechanism that iscompletely different from the conventional growth mechanism in which thecarbon nanotube grows from a metal catalyst as an origin of growth.

[0078] In the carbon nanotube using a metal catalyst as taught byDavydov et al., a porous anodic aluminum oxide film is used to grow thecarbon nanotube in a straight line from a metal catalyst as an origin ofgrowth. It is believed that another reason Davydov et al. uses theporous anodic aluminum oxide film is to provide the metal catalyst inthe form of individual particles. By dispersing particles of the metalcatalyst by gas disposition etc., followed by electric field assistedcarbonization, the carbon nanotube grows in a straight line from theparticles of the metal catalyst as an origin of growth as in Davydov etal., without the porous anodic aluminum oxide film. In these methods,the shape of the carbon nanotube is determined by the particle size ofthe metal particles. Particularly, in the carbon nanotube disclosed inDavydov et al., the shape is largely dependent on growth time(deposition time), and the tip is curled when the growth time is long.Further, in the carbon nanotube disclosed in Davydov et al., the tip ofthe tube is closed.

[0079] The carbon nanotube of the present invention is formed by theadhesion and deposition of carbides on the side wall of the pores of theporous anodic aluminum oxide film, and the shape of the carbon nanotubeis determined by the diameter and length of the pores of the porousanodic aluminum oxide film. Further, the carbon nanotube formed in thepresent invention is not dependent on growth time (deposition time) andalways has the same diameter and the same length. However, the thickness((outer diameter−inner diameter)/2) of the carbon nanotube formed in thepresent invention becomes different depending on the growth time(deposition time).

[0080] As described, the growth mechanism of the carbon nanotube of thepresent invention greatly differs from that of the carbon nanotubedisclosed in Davydov et al. Accordingly, the producing method(transferred onto a template), the shape (tip is opened immediatelyafter the carbon nanotube is formed), and the ease of shape control(always the same diameter and length) of the present invention alsodiffer from those taught in Davydov et al.

[0081] A display of the present invention includes a plurality of carbonnanotubes as a field emission part, an electron source provided with asupport member for supporting each carbon nanotube, and electric fieldapplying means for applying an electric field to each carbon nanotube soas to cause each carbon nanotube to emit electrons, wherein the supportmember is a porous material with large numbers of pores, and each carbonnanotube at least partially adheres to the inner wall of the pores.

[0082] As a result, a highly reliable display with the carbon nanotubesfirmly supported by the support member can be provided.

[0083] An electron source of the present invention includes a carbonnanotube as a field emission part, and a support member for supportingthe carbon nanotube, wherein: the support member is a porous layer,formed on a substrate, having large numbers of through-pores, and thecarbon nanotube is formed in a cylindrical shape inside the pores sothat one end of the carbon nanotube is closed on the side of thesubstrate and an end face of the carbon nanotube on the side of thesubstrate adheres to a surface of the substrate.

[0084] As a result, an electron source with the carbon nanotube firmlyadhering to the support member can be provided. It is therefore possibleto improve the reliability of electrical connection between the carbonnanotube and the support member, when the substrate is used as theelectrode in particular.

[0085] Such a structure of the carbon nanotube in which the carbonnetwork film, with the end on the side of the pore bottom closed,adhered to the substrate is difficult to realize with the techniquetaught in Tokukaihei 8-151207.

[0086] That is, the electron source of the prior art is produced by amethod in which a metal catalyst is provided on the bottom of the poresof the porous anodic aluminum oxide film and the carbon nanotube growsfrom the metal catalyst as an origin of growth. As such, at the bottomof the pores, the metal catalyst particles are two-dimensionally bondedto the under layer, and the carbon nanotube either adheres in the formof a ring or adheres to the under layer via the metal catalyst. Such astate of bonding of the carbon film with respect to the bottom of thepores has been confirmed by the TEM image of a carbon nanotube using afreestanding anodic aluminum oxide film which has been removed from analuminum substrate (such an anodic aluminum oxide film with pores withclosed one end is produced by forming the anodic aluminum oxide film ona barrier layer, without later removing the underlying barrier layer).

[0087] It is preferable in the electron source that the surface of thesupport member adhering to the carbon nanotube be made of at least onekind of material selected from the group consisting of silicon, siliconcarbide, silicon oxide, and silicon nitride.

[0088] A display of the present invention includes: an electron source,which includes a plurality of carbon nanotubes as a field emission partand a support member for supporting each carbon nanotube; and electricfield applying means for applying an electric field to each carbonnanotube so as to cause each carbon nanotube to emit electrons, wherein:the support member is a porous layer, formed on a substrate, havinglarge numbers of through-pores, and each carbon nanotube is formed in acylindrical shape inside the pores so that one end of the carbonnanotube is closed on the side of the substrate and an end face of thecarbon nanotube on the side of the substrate adheres to a surface of thesubstrate. As a result, a display with the carbon nanotube firmlyadhering to the support member can be realized. It is therefore possibleto improve reliability of electrical connection between the carbonnanotube and the support member, particularly when the substrate is usedas the electrode.

[0089] The electron source and display having the foregoing first,third, and fourth features, produced by the producing method having theforegoing second feature, by their physical and chemicalcharacteristics, have an emission characteristic with -an emission startelectric field intensity in a range of from 0.25 V/μm to 0.5 V/μm, andan emission characteristic with an emission current density in a rangeof from 10 mA/cm² to 100 mA/cm² (driving electric field intensity of1V/μm).

[0090] However, there has not been a theoretical support as to thedirect cause of the large current electrons emitted at a low voltagefrom the electron source and display having the foregoing first, third,and fourth features, produced by the producing method having theforegoing second feature using oxygen plasma (etching with oxygenplasma). Thus, no clear cause-and-effect relationship has beenestablished between the foregoing first through fourth features and theemission characteristics of emitting large current electrons at a lowvoltage.

[0091] However, the reasons the electron source produced by theproducing method having the foregoing second feature using oxygen plasmaand having the foregoing first, third, and fourth features emits largecurrent electrons at a low voltage are believed to have been caused by(1) the carbon nanotubes that are polycrystalline (low crystallinity)(first feature), (2) the opened and oxidized tips of the carbonnanotubes by modification of the tips (field emission area) by theoxygen plasma process (carbon-oxygen bonds are selectively formed at thetips of the carbon nanotubes so that the composition of the tips of thecarbon nanotubes is oxygen rich) (second feature), and (3) the anchoredcarbon nanotubes by the scattered particles between the carbon nanotubes(third feature), promoting the low-voltage and large-current fieldemission.

[0092] There has not been any theoretical support as to which of thesefactors is the direct cause. However, according to experiments conductedso far by the inventors of the present invention, the improvement ofemission characteristics is believed to have been greatly influenced bythe first feature, i.e., the polycrystallinity (low crystallinity)associated with carbon nanotube defects (formation of amorphous areas).The defects of the carbon nanotubes are believed to have been broughtabout by the presence of dangling bonds or sp³ hybridization (diamondconfiguration).

[0093] Further, the electron source that emits large current electronsat a low voltage can only be realized by the growth mechanism of thecarbon nanotube distinct to the foregoing producing method of the carbonnanotube, i.e., by the carbon nanotube that is formed by carbondeposition (particularly vapor-phase carbon deposition) in the absenceof a metal catalyst, utilizing the inner wall of the porous material. Itwas impossible to realize the foregoing electron source withconventional carbon nanotubes, for example, such as the carbon nanotubewhich grows from the metal catalyst as an origin of growth inside thepores of the porous layer, and the carbon nanotube that is formed by arcdischarge.

[0094] It is preferable that the electron source of the presentinvention has a resistivity in a range of from 1 kΩ/cm to 100 kΩ/cm anda resistivity higher than that of conventional electron sources. Vacuumdevices, particularly display devices, must be provided with an emissioncurrent control mechanism of some form, and conventional display devicesare provided with a thin film as a resistor layer under the electronsource. In the carbon nanotube electron source of the present invention,the carbon nanotube itself has a high resistance, and thus theconventionally required resistor layer for controlling a current may notbe required depending on device design.

[0095] The following explains the structure of the porous material (orporous layer) used in the producing method of the carbon nanotube andthe producing method of the electron source of the present invention. Inthe producing method of the present invention, the shape of the pores ofthe porous material (or porous layer) is transferred to the carbonnanotube, and therefore the structure of the porous material (or porouslayer) is important.

[0096] The material of the porous material (or porous layer) used in theproducing methods of the present invention, which is not limited as longas it has continuous pores or randomly connected discontinuous pores, ispreferably an insulating material. Such an insulating porous material(or porous layer) can be formed by proving pores, by a method such as ahigh energy ion injection method, in the insulating layer made of aninsulating material, for example, such as glass, organic polymer, orceramic. However, considering cost and convenience, an anodic oxidationmethod is preferable. The anodic oxidation method is a method in which abase member of an oxidizable inorganic material is oxidized by anodicoxidation so as to oxidize the base member and form pores therein.

[0097] Examples of the base member that can be formed into a porousmaterial (or porous layer) by anodic oxidation include tantalum (Ta),silicon (Si), and aluminum (Al). Of these materials, aluminum (Al) ismost preferable as the base member of the porous material (or porouslayer) used in the producing methods of the present invention, becausean aluminum (Al) base member can form pores in a straight line with anano level diameter by anodic oxidation. Further, the anodic aluminumoxide film that is formed by anodic oxidation of aluminum, whensubjected to heat treatment of around 600° C., undergoes a phasetransition to γ-alumina (particles). Thus, the anodic aluminum oxidefilm that is formed by anodic oxidation of aluminum (Al) is consideredto be a suitable material for realizing the electron source with thethird feature of the present invention (individual carbon nanotubes areanchored to one another by the dispersed particles).

[0098] A producing method of the electron source of the presentinvention can also be characterized by the step of forming the anodicoxidation stopping layer under the porous layer. That is, the producingmethod of the electron source of the present invention is a method forproducing an electron source which includes a carbon nanotube as a fieldemission part and a base substrate for supporting the carbon nanotube,and the method includes the steps of forming on the base substrate abase layer made of an oxidizable base material; forming a porous layerwith large numbers of pores by causing the base layer to undergo anodicoxidation; forming the carbon nanotube inside the pores; and forming onthe base substrate an anodic oxidation stopping layer for stoppinganodic oxidation of the base substrate, before the base layer undergoesanodic oxidation.

[0099] The anodic oxidation stopping layer serves as the barrier layerin anodic oxidation and it achieves uniform anodic oxidation in a deviceplane. Thus, an electron source having superior uniformity in emissioncharacteristics in a device plane or an emission area (pixels) can berealized.

[0100] The anodic oxidation stopping layer is preferably silicon,silicon carbide, silicon oxide, or silicon nitride, or a mixture ofthese compounds.

[0101] The carbon nanotube of the present invention has a largeresistance by itself. However, when the device requires a largerresistance by device design, one can structure the device in such amanner that the anodic oxidation stopping layer serves as the highresistor layer. That is, the anodic oxidation stopping layer of thepresent invention may serve as the barrier layer of anodic oxidationduring the production process and as the high resistor layer duringdevice operations.

[0102] Further, the carbon nanotube electron source of the presentinvention, because it emits electrons at a low electric field intensityof around 0.25 V/μm to 0.5 V/μm, electrons are emitted in response tothe applied voltage to the anode electrode. Thus, driving of the carbonnanotube electron source of the present invention requires a drivingmethod that shields the electric field between the cathode electrode andthe anode electrode. The carbon nanotube electron source of the presentinvention is structured to include a gate electrode between the cathodeelectrode and the anode electrode, wherein the gate electrode is drivenby a driving method that shields the electric field from the anodeelectrode. Further, the carbon nanotube electron source of the presentinvention that is driven by such a driving method can use a TFT driverused in conventional liquid crystal devices, and can realize a displaycontaining about 1,000,000 carbon nanotube electron sources integratedin a pixel area which is XY addressed by the cathode electrode and gateelectrode.

[0103] An electron source of the present invention includes a carbonnanotube as a field emission part, wherein the carbon nanotube isdiscontinuous graphite that is divided into micro areas in the tube axisdirection. Another electron source of the present invention includes acarbon nanotube as a field emission part, wherein the carbon nanotubepartially includes an amorphous area in its graphite structure. Withthis structure, the emission start electric field intensity and theoperating voltage (device driving voltage) can be reduced. The amorphousarea can be regarded as an area in which micro crystal defects exist(micro defect area). Thus, the carbon nanotube can be said to includethe micro crystal area by having micro defects (crystal defects) in thegraphite crystal structure.

[0104] Further, the electron source of the present invention can be saidto use a carbon nanotube which includes graphite areas (crystal areas)having sp² bonds, and areas (amorphous areas) which connects onegraphite area to another by a dangling bond. That is, the carbonnanotube is considered to include the graphite areas (crystal areas)having sp² bonds, which are not orderly bonded over the entire area ofthe carbon nanotube making up the electron source but divided into microareas, so that the emission voltage can be reduced. In contrast, theconventional carbon nanotube as disclosed in Tokukaihei 10-12124 has abasic structure of graphite and does not have the amorphous areas.

[0105] Further, in the electron source of the present invention, thecarbon nanotube has a resistivity (specific resistance) preferably in arange of from 1 kΩ·cm to 100 kΩ·cm. That is, the resistivity of thecarbon nanotube is markedly higher than that of a conventional carbonnanotube, for example, such as the carbon nanotube formed by arcdischarge (generally known to have a resistivity of 5×10⁻⁴ kΩ·cm). Withthis characteristic, an electron source that can emit electrons at amarkedly low voltage can be provided. More preferably, the resistivityof the carbon nanotube is in a range of from 50 kΩ·cm to 70 kΩ·cm.

[0106] Further, it is preferable in the electron source of the presentinvention that the field emission part is made up of only carbon atoms.In this way, an electron source with no metal catalyst (metal catalystfree) can be provided.

[0107] Further, it is preferable that the electron source of the presentinvention includes a plurality of carbon nanotubes, and an inorganicmaterial covering the side wall of the carbon nanotubes is provided, soas to electrically insulate the carbon nanotubes from one another. Inthis way, when the carbon nanotubes are to be connected to the cathodeelectrode to make a device, the carbon nanotubes that are integrated inhigh density can be connected to the cathode electrode in parallel toimprove reliability of the device. The inorganic material is preferablyan anodic aluminum oxide film. In this way, stability andreproducibility of orientation control can be improved and reliabilityof the electron source (device) can be further improved.

[0108] The producing method of the electron source of the presentinvention may further include the steps of: forming an inorganicmaterial that has through-pores on the both ends; forming carbonnanotubes on the inner wall of the pores by vapor-phase carbondeposition (pyrolytic carbon deposition) of a gaseous hydrocarbon in thepores of the inorganic material; and depositing the inorganic materialbetween the carbon nanotubes. With this producing method, an electronsource with reduced levels of emission start voltage and operatingvoltage (device driving voltage) can be produced, both inexpensively andconveniently.

[0109] Further, it is preferable in the producing method of the electronsource that the carbon nanotubes be formed using a template of aninorganic material having through-pores on the both ends. In this way, ahighly reliable carbon nanotube with a high level of orientation controlcan be produced stably and with good reproducibility.

[0110] It is preferable in the producing method of the electron sourcethat the step of forming an inorganic material having through-pores onthe both ends is carried out by an anodic oxidation method. That is, thestep of forming an inorganic material having through-pores on the bothends preferably includes the anodic oxidation step. In this way, it ispossible to provide a producing method of an electron source which usesa carbon nanotube that cannot be patterned by the microfabricationtechnique of the semiconductor process.

[0111] Further, the electron source of the present invention mayincludes: a base substrate, provided with a cathode electrode; a highresistor layer, which is provided on the cathode electrode; an inorganicthin film having pores, provided on the high resistor layer; and thecarbon nanotube, which is provided as a field emission part (fieldemission electron source) in the pores, wherein a surface of the carbonnanotube in the vicinity of its tip is modified. With this arrangement,the emission voltage can be further reduced and the electron source canbe driven at a low voltage without being restricted by the carbonnanotube structure and the producing method.

[0112] Further, the producing method of the present invention mayinclude the steps of: forming a cathode electrode wiring on a substrate;forming a high resistor layer on the cathode electrode wiring; formingan inorganic material thin film in a field emission area on the highresistor layer; forming pores through the inorganic material thin film;disposing the carbon nanotube inside the pores; and modifying a surfaceof the carbon nanotube. With this method, an electron source that can bedriven at a low voltage can be produced.

[0113] Further, the producing method of the electron source of thepresent invention may be adapted so that the step of forming the poresthrough the inorganic material thin film is carried out after the stepof forming the inorganic material thin film in the field emission areaon the high resistor layer, and is carried out by anodic oxidation ofthe inorganic material thin film, and the high resistor layer is ananodic oxidation stopping layer for stopping the anodic oxidation whenthe pores are formed by anodic oxidation, and the anodic oxidationstopping layer is made of at least one kind of material which isselected from the group consisting of silicon, silicon carbide, siliconoxide, and silicon nitride. By providing the anodic oxidation stoppinglayer under the carbon nanotube, the anodic oxidation of the upper layerof the inorganic material can be stopped easily, in addition tocontrolling the emission current. As a result, reliability of the devicecan be improved.

[0114] Further, a metal thin film may be provided on the anodicoxidation stopping layer and the metal thin film may be subjected toanodic oxidation. Then, a carbon nanotube may be provided in the poresof the anodic oxidation film to completely oxidize the metal thin filmby anodic oxidation. In this way, the anodic oxidation film can beprevented from being detached, and orientation control and patterning ofthe carbon nanotube can be easily carried out.

[0115] It is preferable in the foregoing producing method that thecarbon nanotube be disposed in the pores of the anodic oxidation filmwithout using a catalyst.

[0116] In this way, an electrically opened state between the carbonnanotube and the cathode electrode can be prevented. Further, comparedwith the producing methods using a catalyst as disclosed in D. N.Davydov et al. and Tokukaihei 10-12124, less cost is required. Further,the production process is simpler than that of the producing method ofthe electron source of Tokukaihei 10-12124, which involves complexproduction processes because the method includes the step of depositinga metal catalyst inside the pores of the anodic oxidation film(electrolytic coloring step).

[0117] It is preferable in the producing method of the electron sourcethat the step of modifying a surface of the carbon nanotube is carriedout by etching using oxygen plasma. In this way, it is possible toprovide a producing method of an electron source that can be driven at ayet lower voltage.

[0118] It is preferable that the electron source having the carbonnanotube as the field emission part be driven by a driving method whichcontrols field emission by inserting a gate electrode between thecathode electrode and the anode electrode between which an electricfield is emitted and by shielding the electric field from the anodeelectrode by the gate electrode. In this way, field emission of a yetlower voltage driving electron source can be controlled.

[0119] The producing method of the carbon nanotube of the presentinvention is a method in which carbon is deposited inside the pores of aporous material with large numbers of pores, so as to form a carbondeposition film of a cylindrical shape, wherein the method includes: theanodic oxidation step for obtaining the porous material; and the heatingstep of not less than 600° C. after the anodic oxidation step.

[0120] This method is different from the method of D. N. Davydov, inwhich acetylene is carbonized at 700° C.

[0121] For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0122]FIG. 1 through FIG. 5 are cross sectional views showing stepsaccording to one embodiment of a producing method of a carbon nanotubeelectron source, in which carbon nanotubes according to the presentinvention are anchored by particles.

[0123]FIG. 6 is a cross sectional view showing the electron source of abipolar tube structure obtained by the foregoing producing method.

[0124]FIG. 7 is a cross sectional view showing an electron source of atripolar tube structure which is obtained from the carbon nanotubeelectron source of the bipolar tube structure shown in FIG. 6.

[0125]FIG. 8 is a cross sectional view schematically showing an exampleof an anodic oxidation device used in the present invention.

[0126]FIG. 9 is a graph showing changes over time of an anodic oxidationcurrent in an anodic oxidation step of the present invention.

[0127]FIG. 10 is a drawing schematically showing an example of avapor-phase carbon deposition device used in the present invention.

[0128]FIG. 11 is an SEM image showing carbon nanotubes that are anchoredby particles according to the present invention, as viewed from above ona 45° angle.

[0129]FIG. 12 is an SEM image showing carbon nanotubes that are anchoredby particles according to the present invention, as viewed directly fromabove.

[0130]FIG. 13 through FIG. 15 are cross sectional views showing steps ofone embodiment of a producing method of a carbon nanotube electronsource, in which a surface of an anodic aluminum oxide film according tothe present invention is partially removed.

[0131]FIG. 16 is a TEM image of the carbon nanotube according to thepresent invention.

[0132]FIG. 17 is a graph showing a Raman spectrum of the carbon nanotubeaccording to the present invention.

[0133]FIG. 18 is a graph showing an X-ray diffraction (XRD) spectrum ofthe carbon nanotube according to the present invention.

[0134]FIG. 19 is a graph showing an X-ray diffraction (XRD) spectrum ofthe carbon nanotube according to the present invention.

[0135]FIG. 20 is a drawing schematically showing a field emissioncharacteristics evaluation device that is used to evaluate fieldemission characteristics of the carbon nanotube electron sourceaccording to the present invention.

[0136]FIG. 21 is a graph showing an example of emission current-appliedvoltage characteristics of the carbon nanotube electron source accordingto the present invention.

[0137]FIG. 22 is a graph showing a Fowler-Nordheim plot of the carbonnanotube electron source according to the present invention.

[0138]FIG. 23 is an SEM image of the carbon nanotube electron sourceaccording to the present invention after an O₂ plasma process, as viewedfrom above on a 45° angle.

[0139]FIG. 24 is an SEM image of the carbon nanotube electron sourceaccording to the present invention after an O₂ plasma process, as vieweddirectly from above.

[0140]FIG. 25 is an SEM image of the carbon nanotube electron sourceaccording to the present invention after a CHF₃ plasma process, asviewed from above on a 45° angle.

[0141]FIG. 26 is an SEM image of the carbon nanotube electron sourceaccording to the present invention after a CHF₃ plasma process, asviewed directly from above.

[0142]FIG. 27 is an SEM image of the carbon nanotube electron sourceaccording to the present invention after an Ar plasma process, as viewedfrom above on a 45° angle.

[0143]FIG. 28 is an SEM image of the carbon nanotube electron sourceaccording to the present invention after an Ar plasma process, as vieweddirectly from above.

[0144]FIG. 29 is an SEM image of the carbon nanotube electron sourceaccording to the present invention before a plasma process, as viewedfrom above on a 45° angle.

[0145]FIG. 30 is an SEM image of the carbon nanotube electron sourceaccording to the present invention before a plasma process, as vieweddirectly from above.

[0146]FIG. 31 is a graph explaining how emission current-applied voltagecharacteristics of the carbon nanotube electron source according to thepresent invention change depending on the presence or absence of theplasma process and the type of plasma process.

[0147]FIG. 32 is a graph showing an XPS spectrum of the carbon nanotubeaccording to the present invention after an O₂ plasma process.

[0148]FIG. 33 is a graph showing an XPS spectrum of the carbon nanotubeaccording to the present invention after a CHF₃ plasma process.

[0149]FIG. 34 is a graph showing an XPS spectrum of the carbon nanotubeaccording to the present invention after an Ar plasma process.

[0150]FIG. 35 is a graph showing an XPS spectrum of the carbon nanotubeaccording to the present invention before a plasma process.

[0151]FIG. 36 is a perspective view showing one embodiment of a displayprovided with the carbon nanotube electron source according to thepresent invention.

[0152]FIG. 37 is a cross sectional view showing one embodiment of adisplay provided with the carbon nanotube electron source according tothe present invention.

[0153]FIG. 38 is a cross sectional view schematically showing anarrangement of conventional carbon nanotubes that have grown from ametal catalyst as an origin of growth.

[0154]FIG. 39 is a cross sectional view schematically showing a randomshape of conventional carbon nanotubes that have grown from a metalcatalyst as an origin of growth.

[0155]FIG. 40 is a graph comparing emission current-applied voltagecharacteristics of a carbon nanotube electron source according to oneembodiment of the present invention and emission current-applied voltagecharacteristics of a conventional carbon nanotube electron source.

BEST MODE FOR CARRYING OUT THE INVENTION

[0156] [First Embodiment]

[0157] Referring to FIG. 1 through FIG. 7, the following will describeone embodiment of a producing method of an electron source (may becalled “carbon nanotube electron source” hereinafter) using a carbonnanotube according to the present invention, i.e., a producing method ofan electron source in which a plurality of carbon nanotubes are anchoredby alumina particles. FIG. 1 through FIG. 7 are step-by-step crosssectional views of the producing method of the electron source that isrealized by a carbon nanotube array in which a plurality of carbonnanotubes are anchored by alumina particles.

[0158] Note that, in the present embodiment, a template (porous layer,porous material) used to form the carbon nanotubes is a porous anodicaluminum oxide film. The template, however, may be of other materialssuch as porous tantalum oxide or porous silicon. Further, the template(porous layer, porous material) may be a film made of a porousinsulating material that is obtained by forming pores through aninsulating film by such means as ion implantation.

[0159] In the producing method of the electron source according to thepresent embodiment, first, as shown in FIG. 1, cathode electrode wiring2 is formed on a base substrate 1, and an anodic oxidation stoppinglayer 3 is subsequently formed over the cathode electrode wiring 2. FIG.1 is a cross sectional view showing the step of forming the cathodeelectrode wiring 2 on the base substrate 1 and then the anodic oxidationstopping layer 3 over the cathode electrode wiring 2.

[0160] The base substrate 1 is an insulating substrate, such as a quartzsubstrate, a glass substrate, or a ceramic substrate, among which thequartz substrate is used in the present embodiment. The cathodeelectrode wiring 2 may be made of an electrode material used forconventional displays, such as chrome (Cr), tungsten (W), nickel (Ni),molybdenum (Mo), niobium (Nb), and copper (Cu). In the presentembodiment, the material of the cathode electrode wiring 2 is copper.The thickness of the cathode electrode wiring 2, which is decidedaccording to such factors as resistivity or wiring resistance, is about0.1 μm to 1 μm. The cathode electrode wiring 2 is suitably patterned toa predetermined shape (e.g., a plurality of discrete portions as shownin FIG. 1).

[0161] The anodic oxidation stopping layer 3 is a layer for stoppingprogression of anodic oxidation of an aluminum film 4 onto the cathodeelectrode wiring 2. The material of the anodic oxidation stopping layer3 is preferably a highly resistive material, capable of limiting theemission current in addition to stopping the anodic oxidation. That is,the anodic oxidation stopping layer 3 preferably serves also as a highresistor layer that limits the emission current. However, in the casewhere the carbon nanotube of the present invention has a resistance (thecarbon nanotubes of the present embodiment have a specific resistance ashigh as 1 kΩ/cm to 100 kΩ/cm) that coincides with a resistance that isrequired to limit the current in the device design of the electronsource, the anodic oxidation stopping layer 3 is not necessarilyrequired to serve as a high resistor layer. Further, the anodicoxidation stopping layer 3 preferably has a coefficient of thermalexpansion that is substantially equal to that of an anodic aluminumoxide film 5. This prevents the anodic aluminum oxide film 5 from beingdetached from the anodic oxidation stopping layer 3 during the processof vapor-phase carbon deposition.

[0162] Further, as taught in Japanese Unexamined Patent Application No.11-194134, the under layer material of the anodic aluminum oxide filmmay be made of metal such as titanium (Ti), niobium (Nb), or molybdenum(Mo), to realize the anodic oxidation stopping layer 3.

[0163] In the present embodiment, the anodic oxidation stopping layer 3is an amorphous silicon film (non-doped sputtered silicon) which has thefunction of a high resistor layer. Results of experiment by theinventors of the present invention have shown that the anodic oxidationstopping layer 3 is preferably made of silicon materials, among whichsilicon, silicon carbides (SiC), silicon oxides, silicon nitrides, and amixture of these are particularly preferable in terms of stopping theanodic oxidation in the anodic oxidation step. These silicon compoundsare also preferable in respect to their resistance and serve as a highresistor layer. Further, these silicon compounds are also preferable asa base layer for supporting carbon nanatubes 8 in contact with an endface thereof.

[0164] When using silicon carbides as a material of the anodic oxidationstopping layer 3, the silicon carbides may be deposited to form theanodic oxidation stopping layer 3, or the silicon film after depositionmay be converted to a carbide by the vapor-phase carbon deposition informing the carbon nanotubes. When using silicon oxides, siliconnitrides, or a mixture of these silicon compounds as the material of theanodic oxidation stopping layer 3, these materials are deposited by achemical vapor deposition (hereinafter “CVD”) method or a sputteringmethod, which can be easily carried out. In the present embodiment, theanodic oxidation stopping layer 3 is designed to have a resistance thatexceeds 10⁸Ω (high resistance). In order to prevent shorting of thecathode electrode wiring 2, the anodic oxidation stopping layer (highresistor layer) 3 is preferably patterned into a predetermined shapeaccording to the patterns of the cathode electrode wiring 2 (e.g.,patterns that cover the cathode electrode wiring 2 by surrounding it, asshown in FIG. 1).

[0165] Thereafter, as shown in FIG. 2, the aluminum film 4 is formed onthe anodic oxidation stopping layer (high resistor layer) 3, followed bypatterning of the aluminum film 4 such that the aluminum film 4 remainsin areas over the cathode electrode wiring 2.

[0166]FIG. 2 is a cross sectional view showing the step of forming thealuminum film 4 on the anodic oxidation stopping layer (high resistorlayer) 3. Note that, the present embodiment uses the aluminum film 4because the template is the anodic aluminum oxide film. Depending on thetype of template, a tantalum film or a silicon film may be used.Further, the template may be prepared from an insulating film made of aninsulating material such as a silicon oxide film, an alumina film, or anorganic film, by forming micro pores therethrough by a method such asthe ion implantation method.

[0167] The aluminum film 4 used to form the anodic aluminum oxide film 5preferably has a purity of 99% or higher and preferably has a thicknessof not less than 1 μm to accommodate pores. In the present embodiment,the thickness of the aluminum film 4 is 2 μm. The aluminum film 4 can beformed by a method using a vacuum device, such as a sputtering method ora vapor deposition method, when the thickness of the aluminum film 4 isnot less than 1 μm and less than 10 μm, or particularly from about 1 μmto about 5 μm. However, deposition of the aluminum film 4 becomesdifficult when the thickness is 10 μm or more. The aluminum film 4 witha thickness of 10 μm or more can be preferably formed by using analuminum foil of a predetermined thickness as the aluminum film 4 andattaching the aluminum foil on the anodic oxidation stopping layer (highresistor layer) 3 or the cathode electrode wiring 2 by a method such asan electrostatic bonding method. In either case, the surface of thealuminum film 4 is preferably mirror-finished. Considering this surfaceroughness of the aluminum film 4, it can be said that the filmdeposition method such as a sputtering method or a vapor depositionmethod is a preferable method of forming the aluminum film 4, because itonly requires a single step to obtain aluminum film 4 with a mirrorfinish, but does not require a step of electrolytic polishing to obtainmirror-finished aluminum film 4, which is required in bonding analuminum foil or an aluminum substrate on the anodic oxidation stoppinglayer (high resistor layer) 3 or the cathode electrode wiring 2 by theelectrostatic bonding method.

[0168] It should be noted here that instead of patterning the aluminumfilm 4, patterning may be carried out after forming the anodic aluminumoxide film 5 in FIG. 3. The patterning before the anodic oxidation step(patterning of the aluminum film 4) has a merit over the patterningafter the anodic oxidation step (patterning of the anodic aluminum oxidefilm 5) in that sharper patterns are obtained. The demerit of thepatterning after the anodic oxidation step (patterning of the anodicaluminum oxide film 5) is poorer uniformity in pattern edge of theanodic aluminum oxide film 5. The patterning of the aluminum film 4 canbe readily carried out by wet etching using a mixture of phosphoricacid, nitric acid, and acetic acid.

[0169] Subsequently, as shown in FIG. 3, the aluminum film 4 on theanodic oxidation stopping layer (high resistor layer) 3 is subjected toanodic oxidation to obtain the anodic aluminum oxide film 5 with largenumber of pores 6.

[0170]FIG. 3 is a cross sectional view showing the step of anodicoxidation of the aluminum film 4 on the anodic oxidation stopping layer(high resistor layer) 3. It is required that the aluminum film 4 becompletely oxidized by the anodic oxidation. Avoiding residual aluminumfilm 4 ensures a time margin for the heat treatment in the producingsteps. FIG. 8 schematically shows an anodic aluminum oxidation deviceused in the present embodiment. A target sample (aluminum film 4) ofanodic oxidation is disposed as an anode 12 in a chemical solution 14,and a cathode 13 is provided as a counter electrode opposite the anode12 in the chemical solution 14. The chemical solution 14 may be sulfuricacid, oxalic acid, and the like. Between the anode 12 and the cathode 13are provided a power supply 16 and an ammeter 17. Applying a positivelybiased voltage from the power supply 16 to the anode 12 sets off anodicoxidation. The chemical solution 14 is stirred with a stirrer 15 andmaintained at a desired temperature in a thermostat bath 18. Theconditions of anodic oxidation of the aluminum film 4 should be suitablyoptimized so that the pores 6 are formed according to the tip diameterof the carbon nanotubes designed by a person ordinary skilled in theart. In the present embodiment, the designed tip diameter (averagediameter) of the carbon nanotubes was 30 nm, and a constant voltage of20 V was applied in a sulfuric acid solution at 0° C. so as to carry outanodic oxidation for 20 minutes. The anodic oxidation completelyoxidized the aluminum film 4 of 2 μm thick, and produced the anodicaluminum oxide film 5 of 2.8 μm thick, having pores 6 with an averagediameter of 30 nm and a density of around 10¹⁰/cm². The completion ofanodic oxidation of the aluminum film 4 can be easily found from acurrent change as a function of time (measured with the ammeter 17), asshown in FIG. 9. FIG. 9 schematically depicts a change in current as afunction of time in the anodic oxidation step. In FIG. 9, a firstcurrent-time characteristic 19 indicates the current-time characteristicof a bulk aluminum film (e.g., aluminum plate), and a secondcurrent-time characteristic 20 indicates the current-time characteristic(characteristic of anodic oxidation) of a thin film (deposited film),i.e., the aluminum film 4 of the present embodiment. The current-timecharacteristic 20 of the thin film aluminum film 4 shows such acharacteristic that the current rises abruptly in response toapplication of a voltage before it levels off to a substantiallyconstant rate. Upon near completion of the anodic oxidation of the thinfilm aluminum film 4, the current suddenly decreases to only severalpercent of the initially observed current value. The end point of thethin film aluminum film 4 is observable by visual inspection byobserving a change in color of the surface of the aluminum film 4 fromthe original silver to the color of the underlying anodic oxidationstopping layer 3. On the other hand, the current-time characteristic 19of the anodic oxidation of the bulk aluminum film shows an abruptcurrent increase in response to voltage application before it decreasesat a substantially constant rate. In this manner, the current-timecharacteristic 20 of the anodic oxidation of the thin film aluminum film4 and the current-time characteristic 19 of the anodic oxidation of thebulk aluminum film show completely different behaviors. Monitoring ofthe current-time characteristics of the anodic oxidation is desirable inmanaging the anodic oxidation step of the thin film aluminum film 4 ofthe present embodiment, and it contributes a great deal toreproducibility of the anodic oxidation. Note that, the current, insteadof the voltage, may be held constant. In this case, a voltmeter, insteadof the ammeter 17, can be used to monitor the current-timecharacteristics and to find the end point of the anodic oxidation.

[0171] Note that, in order to improve uniformity of the tubes 6 of theanodic aluminum oxide film 5, the anodic oxidation may be carried out intwo steps. That is, in the first step, the aluminum film 4, about 0.5 μmthick, is subjected to anodic oxidation (for 5 minutes in a sulfuricacid solution at 0° C. under an applied voltage of 20 V), and the anodicoxidized film is subsequently detached by wet etching (in a 0.5 weight %hydrofluoric acid aqueous solution, at room temperature, for about 2minutes). Subsequently, in the second step, remains of the aluminum film4 is completely oxidized by further anodic oxidation (for 15 minutes ina sulfuric acid solution at 0° C. under applied voltage of 20 V). Byexperiment, this was proven to greatly improve uniformity of the pores 6of the anodic aluminum oxide film 5. Another technique to uniformly formthe tubes as in the forgoing method is taught in (H. Masuda et al.,Appl. Phys. Lett., 71, 19, 2770 (1997)). Further, the chemical solutionof anodic oxidation may be oxalic acid, phosphoric acid, or the like.Using oxalic acid in particular enables the pores to be formed in anaverage diameter of about 30 nm, as in the foregoing example, by theapplication of a voltage of around 25 V at room temperature.

[0172] Thereafter, the anodic aluminum oxide film is patterned so thatthe pores 6 reach the anodic oxidation stopping layer 3. Care must betaken for the patterning of the anodic aluminum oxide film 5 to avoidetching residue or pattern chipping or the like. In the presentembodiment, the anodic aluminum oxide film 5 is patterned by a wetetching method in combination with an ultrasonic washing method.Examples of etchants used in the wet etching include: a hydrofluoricacid (HF) aqueous solution; an aqueous solution of a mixture ofphosphoric acid (H₃PO₄) and hydrochloric acid (HCl); an aqueous solutionof a mixture of phosphoric acid (H₃PO₄), nitric acid (HNO₃), and aceticacid (CH₃COOH); and a sodium hydroxide aqueous solution (NaOHaq), amongwhich the aqueous solution of a mixture of phosphoric acid (H₃PO₄) andhydrochloric acid (HCl) is preferable. The weight concentration (weightof phosphoric acid and hydrochloric acid/total weight) of the aqueoussolution of a mixture of phosphoric acid (H₃PO₄) and hydrochloric acid(HCl) is preferably 10 weight % to 80 weight %. With a weightconcentration of the mixed acid aqueous solution at or above 80 weight%, resist damage is observed. With a weight concentration of the mixedacid aqueous solution at or below 10 weight %, etching residue of theanodic aluminum oxide film becomes prominent. In the present embodiment,the anodic aluminum oxide film 5 is wet etched with an etchant whoseweight concentration of the mixed acid is 40 weight % (phosphoric acid(H₃PO₄)/hydrochloric acid (HCl)/pure water (H₂O)=3:1:6). Subsequent tothe wet etching, ultrasonic washing (power: 100 W, frequency: 40 kHz) iscarried out. The purpose of ultrasonic washing is to remove etchingresidue of the anodic aluminum oxide film 5. However, ultrasonic washinglonger than 10 minutes causes pattern chipping. Experiments have shownthat serious pattern chipping of the anodic aluminum oxide film occurswhen the ultrasonic washing exceeds 5 minutes. The optimum balance ofwet etching and ultrasonic washing should be attained by observing thestate of etching residue and the state of pattern chipping of the anodicaluminum oxide film 5. In the present embodiment, the anodic aluminumoxide film 5 is patterned by etching for 5 minutes at 70° C., using a 40weight % mixed acid of phosphoric acid (H₃PO₄) and hydrochloric acid(HCl) as an etchant, followed by ultrasonic washing for 1 minute.

[0173] Thereafter, the anodic aluminum oxide film 5 is subjected tovapor-phase carbon deposition so as to form a carbon deposition film 7within the tubes 6 of the anodic aluminum oxide film (template) 5, asshown in FIG. 4. The carbon deposition film 7 adheres to the inner wallof the pores 6 to form carbon nanatubes 8 having substantially the sameouter diameter as that of the pores 6. The carbon nanatubes 8, thoughnot shown, are hollow tubes with a closed end on the side of the anodicaluminum oxide film 5, and the entire end face on the side of the anodicaluminum oxide film 5 is in contact with a surface of the anodicaluminum oxide film 5. Further, as shown in FIG. 4, the carbondeposition film 7 adheres not only to the inner wall of the pores 6 butalso to the surface of the anodic aluminum oxide film 5.

[0174]FIG. 4 is a cross sectional view showing the step of vapor-phasecarbon deposition of the carbon deposition film 7 on the pores 6 of theanodic aluminum oxide film (template) 5. As a vapor-phase carbondeposition device, a heat CVD device of a basic structure as shown inFIG. 10 can be used. That is, the base substrate 1, the cathodeelectrode wiring 2, the anodic oxidation stopping layer 3, and theanodic aluminum oxide film 5 shown in FIG. 3 are used as a sample 21 andplaced in a quartz reaction tube 22. The vapor-phase carbon depositionis carried out by heating the quartz reaction tube 22 with the sample 21to a predetermined temperature using a heater 23, followed by chargingthe quartz reaction tube 22 with hydrocarbon gas as source gas 24 fromone end of the quartz reaction tube 22. This sets off pyrolysis of thehydrocarbon gas (source gas 24) and generates carbon. The carbondeposits on the surface of the sample 21 and forms the carbon depositionfilm 7 thereon. The gas flown through the quartz reaction tube 22 isdischarged out of the reaction system (out of the quartz reaction tube22) as discharge gas 25. The vapor-phase carbon deposition device (FIG.10) of the present embodiment is designed to satisfy such specificationsthat a constant temperature is maintained in the quarts reaction tube 22at least in an area where the sample 21 is placed, and that a constantpressure is maintained inside the quartz reaction tube 22. Thevapor-phase carbon deposition in the present embodiment was carried outunder the following conditions: propylene was used as the source gas 24(2.5% in nitrogen); the source gas 24 (propylene) was flown through thequartz reaction tube 22 for 3 hours; and inside the quartz reaction tube22 was heated at a temperature of 800° C. The heating temperature insidethe quartz reaction tube 22 in the vapor-phase carbon deposition shouldbe a temperature that induces pyrolysis of the source gas (hydrocarbon)24. When propylene is used as the source gas 24 as in the presentembodiment, a temperature range of 600° C. to 900° C. is preferable. Thesource gas 24 is not just limited to propylene, and other kinds ofhydrocarbon gas such as acetylene may be used as well. In the case ofvapor-phase carbon deposition using plasma assist, the vapor-phasecarbon deposition may be carried out with a mixture of methane gas andhydrogen gas at a temperature of about 650° C. Such vapor-phase carbondeposition using plasma assist was carried out in the following manner,for example. The sample 21 was heated to about 650° C. and a microwaveof 2.45 GHz was generated in the quartz reaction tube 22. Inside thequartz reaction tube 22 was charged with a mixture of methane gas andhydrogen gas (methane:hydrogen=1:4) and a DC bias of about 150 V wasapplied inside the quartz reaction tube 22 to continue the process for10 minutes. With such vapor-phase carbon deposition method using plasmaassist, the carbon nanatubes 8 can be formed at a relatively lowtemperature.

[0175] Subsequently, as shown in FIG. 5, the carbon deposition film 7adhering on a surface of the anodic aluminum oxide film 5 was removed,so as to separate the carbon nanatubes 8 into individual pieces and tomodify the surface on the tip of the carbon nanatubes 8. FIG. 5 is across sectional view showing the step of removing the carbon depositionfilm 7 adhering on a surface of the anodic aluminum oxide film 5 toseparate the carbon nanatubes 8 into individual pieces.

[0176] The carbon deposition film 7 was removed by dry etching usingplasma (hereinafter referred to as “plasma process”). By the plasmaprocess, not only the carbon deposition film 7 on the anodic aluminumoxide film 5 is removed but the surface on the tip of the carbonnanatubes 8 is selectively modified. With the modification of the carbonnanatubes 8, the field emission characteristics of the carbon nanatubes8 can be improved. It can be said that this improvement of fieldemission characteristics by the surface modification process is achievedfor the first time by the arrangement of the present embodiment whereinside walls of the carbon nanatubes 8 are covered with the anodicaluminum oxide film 5, and it is the effect distinct to the carbonnanatubes 8 that are formed by the vapor-phase carbon deposition methodusing the template. Note that, in the present embodiment, the plasmaprocess uses the reactive ion etching (RIE).

[0177] The etching gas that can be used for the plasma process includesoxygen, argon, helium, hydrogen, nitrogen, carbon trifluoride, andcarbon tetrafluoride. The etching gas is preferably oxygen. Namely, theplasma process is preferably an oxygen plasma process. This is becausethe field emission characteristics of the carbon nanatubes 8 of thepresent embodiment become particularly effective when the oxygen plasmaprocess is carried out, as clearly indicated by the field emissioncharacteristics (I-V characteristics) of the plasma-treated carbonnanatubes 8 of FIG. 31 to be described later.

[0178] Note that, in order to perform surface modification only on thetip of the carbon nanatubes 8, it is preferable that the pores of theanodic aluminum oxide film 5 (template) have open ends. With the anodicaluminum oxide film 5 (template) having such a structure, side surfacesof the carbon nanatubes 8 are protected by the anodic aluminum oxidefilm 5 (template) and are uninfluenced at all by the surfacemodification process. In the present embodiment, the oxygen plasmaprocess is carried out to perform surface modification only on the tipof the carbon nanatubes 8. With the absence of the anodic aluminum oxidefilm 5 (template) on side surfaces of the carbon nanatubes 8, a graphitelayer (carbon network film) on the side surfaces is etched by the oxygenplasma and this prevents formation of an electron source structure. Bythus covering side surfaces of the carbon nanatubes 8 with the anodicaluminum oxide film 5 (template) to carry out the surface process(oxygen plasma process) as in the present embodiment, only the tip edgeof the carbon nanatubes 8 can be subjected to the surface modification.

[0179] Subsequently, as shown in FIG. 6, the anodic aluminum oxide film(template) 5 is partially removed, leaving the alumina particles 9, andthe carbon nanotubes 8 are exposed. As a result, the carbon nanatubes 8become disposed parallel to one another (orientation control) by thealumina particles 9 that are scattered between the carbon nanatubes 8.In addition, the side surfaces of adjacent carbon nanatubes 8 are boundto one another.

[0180] The anodic aluminum oxide film 5 is removed preferably by wetetching using an etchant such as an aqueous solution of alkali,phosphoric acid, or hydrofluoric acid. The type of etchant used in wetetching and the processing temperature should be selected according tothe temperature of a heat treatment in the vapor-phase carbondeposition. That is, when the temperature of a heat treatment in thevapor-phase carbon deposition is around 800° C., heat alkali etching ispreferable. When the temperature of a heat treatment in the vapor-phasecarbon deposition is below 800° C., an alkali treatment or ahydrofluoric acid treatment at around room temperature may be carriedout. In the case of a hydrofluoric acid treatment, because of its highetching rate, a dilute hydrofluoric acid aqueous solution diluted to 1weight % or less is preferably used. When the etching time is short, thetips of the carbon nanatubes 8 cannot be exposed. On the other hand,when the etching time is too long, the carbon nanatubes 8 becomedisoriented and the field emission characteristics become poor. In thepresent embodiment, an aqueous solution of 20 weight % sodium hydroxidewas used to carry out heat alkali etching for 2 hours at 150° C.

[0181] As noted above, the anodic aluminum oxide film (template) 5 hasgone through the heat CVD process between the state shown in FIG. 4 andthe state shown in FIG. 5, and a temperature range of the heat CVDprocess is from 600° C. to 900° C. The phase transition temperature ofalumina from the amorphous phase to γ-alumina is known to be around 600°C. When the temperature of the heat CVD process is from 600° C. to 900°C., it is envisaged that the anodic aluminum oxide film 5, which is inthe amorphous phase when it is formed, has partially made a transitionto γ-alumina by the heat CVD process, by the time the process reachesthe state of FIG. 5. In the present embodiment, it is believed that theγ-alumina phase after the transition remain in the anodic aluminum oxidefilm 5 as the alumina particles 9, which, because of its highselectivity ratio for the etchant (sodium hydroxide) used to remove theanodic aluminum oxide film 5, become the alumina particles 9 that anchorthe carbon nanatubes 8.

[0182] The electron source of the present invention utilizes suchalumina particles 9 as a constituting element. FIG. 11 (electronmicrograph image viewed from side on an angle) and FIG. 12 (electronmicrograph image viewed from top) clearly show that the aluminaparticles 9 anchor the carbon nanatubes 8 that are integrated.Proceeding the removal of the anodic alumina oxide film 5 causes thecarbon nanatubes 8 to disorient themselves and the field emissioncharacteristics suffer. Thus, the amount of anodic aluminum oxide film 5removed should be optimized so that the field emission characteristicsbecome optimal.

[0183] The carbon nanotube electron source of a bipolar tube structureas shown in FIG. 6 can be obtained in this manner. Such a carbonnanotube electron source can be used in vacuum micro devices, forexample, such as a cold cathode ray tube and a fluorescent display tube.

[0184] Referring to FIG. 7, the following explains a producing method ofa carbon nanotube electron source of a tripolar tube structure. FIG. 7shows a carbon nanotube electron source of a tripolar tube structure. Ina producing method of the carbon nanotube electron source of a tripolartube structure of the present embodiment, an insulating substrate 10provided beforehand with gate electrode wiring 11 on one side and a gateopening 10 a is bonded, with the side of the gate electrode wiring 11facing out, to the carbon nanotube electron source of the bipolarstructure shown in FIG. 6. The gate opening 10 a is provided over thearea of the carbon nanotube electron source of the bipolar structure ofFIG. 6 where the carbon nanatubes 8 are formed. The bonding can be madeby a conventional method such as an electrostatic bonding method. Such aproducing method is suitable to produce a carbon nanotube electronsource of a large area, because it does not require a vacuum device orphotolithography and thus enables a carbon nanotube electron source of alarge area to be produced conveniently and inexpensively.

[0185] The material of the gate electrode wiring 11 may be molybdenum(Mo), tungsten (W), and niobium (Nb). The material of the insulatingsubstrate 10 may be glass, ceramic, and organic polymers. The gateopening 10 a may be processed in a size of about 50 μm. The diameter ofthe gate opening 10 a is preferably several tens of microns to severalhundreds of microns, depending on device design.

[0186] Note that, the carbon nanotube electron source of the tripolartube structure can also be formed by a semiconductor process. Aproducing method of the tripolar tube structure using the semiconductorprocess will be described in detail in a Second Embodiment.

[0187] The carbon nanotube electron source which are anchored by theparticles of the present embodiment produced in the described manner hasa configuration as shown in FIG. 11 and FIG. 12. FIG. 11 is an image ofa scanning electron microscope (hereinafter referred to as SEM) when thecarbon nanotube electron source of the present embodiment is viewed froma 45° angle from above. FIG. 12 is a SEM image of the carbon nanotubeelectron source of the present embodiment viewed directly from above. Asis clear from these SEM images, the carbon nanotube electron source ofthe present embodiment has a large number of carbon nanotubes that arehighly integrated in an orientation-controlled arrangement, wherein theparticles (γ-alumina; seen white in the SEM images) that are scatteredbetween the carbon nanotubes bind side faces of the carbon nanotubes.Note that, the carbon nanotubes are carbon nanotubes of at least onelayer of a cylindrical carbon network film, wherein the carbon networkfilm has a polycrystalline structure of a plurality of divided crystalareas in a tube axis direction (see FIG. 7 and FIG. 11).

[0188] The carbon nanotube electron source as taught by W. A. de Heer isa casting film with carbon nanotubes and is not the carbon nanotubeelectron source of the controlled orientation. That is, when such acarbon nanotube electron source is used in a device, the problem ofnon-uniform field emission occurs. In contrast, the carbon nanotubeelectron source of the present embodiment, because of orientationcontrol of the carbon nanotubes, has superior field emission uniformity.

[0189] In a carbon nanotube electron source of D. N. Davydov, the underlayer of the anodic aluminum oxide film is aluminum, and therefore theanodic aluminum oxide film is easily detached by the heat process offorming the carbon nanotubes. In contrast, in the electron source of thepresent embodiment, the under layer of the anodic aluminum oxide film 5is a non-doped sputter silicon film (anodic oxidation stopping layer 3)and therefore the anodic aluminum oxide film 5 is less likely to bedetached from the under layer by the heat process of forming the carbonnanotubes. As a result, an electron source with high reliability can beprovided.

[0190] [Second Embodiment]

[0191] An electron source of the present embodiment differs from that ofthe First Embodiment in that, unlike the First Embodiment in which thecarbon nanotubes are anchored by the particles, a surface of the anodicaluminum oxide film is partially removed to make up a carbon nanotubearray.

[0192]FIG. 13 through FIG. 15 show a producing method of a carbonnanotube electron source of the present embodiment. In the producingmethod of the tripolar tube structure of the present embodiment, avacuum device and photolithography, which are known in a conventionalsilicon semiconductor process is used. However, the insulating substrate10 provided with the gate electrode wiring 11 may be bonded, asexplained with reference to FIG. 7 in the First Embodiment.

[0193]FIG. 13 is a cross sectional view showing a step of vapor-phasecarbon deposition of a carbon deposition film 7 on pores 6 of an anodicaluminum oxide film (template) 5. Niobium (Nb) is formed as cathodeelectrode wiring 2 on a quartz substrate, i.e., a base substrate 1, andnon-doped silicon (Si) is formed as an anodic oxidation stopping layer(high resistor layer) 3 on the cathode electrode wiring 2. On the anodicoxidation stopping layer 3 is provided the anodic aluminum oxide film(template) 5 which is formed by the anodic oxidation of an aluminum film4. The carbon deposition film 7 adheres on surfaces of the anodicaluminum oxide film (template) 5 and on the inner wall of the pores.

[0194]FIG. 14 is a cross sectional view showing a step of forming acarbon nanotube electron source provided with a gate opening. First, thegate insulating layer 10 is formed using an insulating material such asglass, ceramic, organic polymers, mica, and crystalline quartz. In thepresent embodiment, the gate insulating film 10 was made from an SOG(Spin on Glass; coated glass) film. The gate insulating film 10 of SOGwas formed by spin-coating an SOG film material (glass based pastematerial) dissolved in a solvent followed by baking. The thickness ofthe gate insulating film 10 made from an SOG film after baking was 1 μm.Note that, the gate insulating film 10 may be formed to a thickness ofaround 100 μm by screen printing a paste of a silicon oxide basedinsulating material several times. Then, a material of the gateelectrode wiring 11 was deposited on the gate insulating film 10 to forma conductive layer. As a material of the gate electrode wiring 11, ametal material having a high melting point such as molybdenum (Mo),tungsten (W), or niobium (Nb) is preferable. In the present embodiment,niobium (Nb) was deposited to a thickness of 1500 Å. The gate electrodewiring 11 may also be formed by screen printing using a metal paste.Considering formation of the gate opening, it is preferable that thematerial of the gate electrode wiring 11 and the material of the gateinsulating layer 10 are a combination of materials with a greatlydiffering etching selectivity ratio. In the present embodiment, aphotoresist with an open window for the gate opening was formed. Afterexposure, hydrofluoric-nitric acid (a mixture of hydrofluoric acid andnitric acid) having a large selectivity ratio for the SOG was used toprocess (etch) a conductive film (material of the gate electrode wiring11) at the gate opening, and dilute hydrofluoric acid (1 weight % to 5weight % aqueous solution of hydrofluoric acid) was used to process(etch) the gate insulating film 10 at the gate opening, so as to formthe gate opening (hole). Note that, the etching removal may be carriedout by a combination of dry etching and wet etching, so as to minimizeside etching within the gate opening. For example, after the majority ofthe gate insulating film 10 has been removed by dry etching, the gateinsulating layer 10 of several nm may be removed by wet etching.

[0195] Subsequently, the carbon deposition film 7 on the surface of theanodic aluminum oxide film (template) 5 was removed. The carbondeposition film 7 was removed by reactive ion etching (RIE) using oxygenplasma, as in FIG. 5. Removal of the carbon deposition film 7 may becarried out before forming the gate opening. However, when the carbondeposition film 7 is to be removed before forming the gate opening,caution must be taken not to contaminate the tips of the carbonnanotubes.

[0196]FIG. 15 is a cross sectional view showing a step after the tips ofthe carbon nanotubes have been exposed. The carbon nanatubes 8 wereexposed by wet etching using dilute hydrofluoric acid (1 weight % to 5weight % aqueous solution of hydrofluoric acid). The etching amount ofthe anodic aluminum oxide film (template) 5 should be equal to orgreater than the spacing between the carbon nanotubes. In the presentembodiment, the spacing between the carbon nanotubes is 30 nm, and theetching amount of the anodic aluminum oxide film (template) 5 was about50 nm (30 nm or greater is acceptable).

[0197] The present embodiment uses the glass based insulating material(SOG) as the gate insulating layer 10, and therefore there is apossibility of a side etching phenomenon whereby the gate insulatinglayer 10 is removed (etched) at the same time as the anodic aluminumoxide film 5 (porous alumina). The problem of side etching can beavoided by changing the material of the gate insulating layer 10 or bychanging the etchant used to etch the anodic aluminum oxide film 5 to amaterial with a higher selectivity ratio for the gate insulating layer10.

[0198] A feature of the carbon nanotube electron source of the tripolartube structure thus prepared is the structure in which the diameter ofthe gate opening becomes smaller as it approaches to the electronsource, and the field emission area (pixel in the case of a display) ismade of an insulating material (anodic aluminum oxide film) differentfrom the gate insulating layer 10.

[0199] [Third Embodiment]

[0200] The present embodiment describes a structure of a carbonnanotubes of the present invention. The structure of the carbonnanotubes was analyzed by characterization of crystallinity, whichinvolved observation under a transmission electron microscope(hereinafter referred to as TEM), and analysis by X-ray diffraction(XRD) spectrometry and Raman spectrometry, and measurement ofresistivity.

[0201]FIG. 16 is a TEM image of a carbon nanotube sample of the presentembodiment; FIG. 17 is a Raman spectrum of a carbon nanotube sample ofthe present embodiment; and FIG. 18 and FIG. 19 are X-ray diffractionspectra of a carbon nanotube sample of the present embodiment.

[0202] The carbon nanotube sample for the analysis of the carbonnanotube structure was prepared in the following manner. An aluminumsubstrate that has been electropolished was subjected to anodicoxidation in a 20 weight % aqueous solution of sulfuric acid in an icedwater bath (0° C.) under an applied voltage of 20 V for 2 hours, usingan anodic oxidation device shown in FIG. 8, so as to form an anodicaluminum oxide film (porous anodic aluminum oxide film) with largenumbers of pores. The current-time characteristics of anodic oxidationare as shown by current-time characteristics 19 in FIG. 9. The anodicaluminum oxide film (thickness of about 75 μm, and the diameter of poresof about 30 nm) thus prepared was removed from the aluminum substrate.The anodic aluminum oxide film can be removed by applying a reversedvoltage of the applied voltage for 10 minutes to the aluminum substratewith the anodic aluminum oxide film in a sulfuric acid aqueous solution,using the anodic oxidation device shown in FIG. 8. The anodic aluminumoxide film thus removed was subjected to vapor-phase carbon depositionusing a heat CVD device of FIG. 10 (anodic aluminum oxide film was setin a quartz tube) under the conditions of vapor-phase carbon depositionin the step shown in FIG. 4 of the First Embodiment (2.5% propylene innitrogen, 800° C., 3 hours), so as to form carbon nanotubes in the poresof the anodic aluminum oxide film and thus obtain the carbon nanotubesample with the anodic aluminum oxide film (hereinafter referred to ascarbon nanotube sample for structural analysis).

[0203] Note that, simultaneously with the formation of the carbonnanotubes, the carbon deposition film is formed on the surface of theanodic aluminum oxide film. The interface of the aluminum substrate andthe anodic aluminum oxide film may be provided with an anhydrous aluminalayer called a barrier layer (anodic oxidation stopping layer). In thecase where the anhydrous alumina layer (barrier layer) is formed, theanodic aluminum oxide film that was removed is allowed to stand for anhour in a sulfuric acid solution so as to dissolve the barrier layer.

[0204] The anodic aluminum oxide film was completely removed by wetetching (150° C., 3 hours) using a 20 weight % sodium hydroxide aqueoussolution with respect to the carbon nanotube sample for structuralanalysis, so as to isolate the carbon nanotube sample.

[0205] The carbon nanotube sample was then observed under TEM. FIG. 16shows an image of the carbon nanotube sample observed under TEM. As isclear from FIG. 16, the carbon nanotubes of the present embodiment aremulti-walled carbon nanotubes with multi-walls (multiple layers) havinga diameter of about 26 nm and a thickness of about 6 nm. It can also beseen that the carbon network film making up the multi-walls has apolycrystalline structure with divided micro crystal areas interposedbetween amorphous areas. The micro crystal areas are disposedsubstantially one dimensionally in a tube axis direction and the sizethereof in the tube axis direction is several nm. Such a structure isvery different from that of conventional carbon nanotubes, which do nothave the structure in which the carbon network film is divided intomicro areas. The structural difference becomes even more prominent inbulk graphite.

[0206] In the description that follows, the carbon network film of thecarbon nanotubes of the present embodiment is identified and the size ofthe small areas is quantified.

[0207]FIG. 17 is a Raman spectrum of the carbon nanotube sample forstructural analysis (with the anodic aluminum oxide film). As clearlyindicated by FIG. 17, the carbon nanotube of the present embodiment haveRaman spectrum peaks in the vicinities of 1600 cm⁻¹ and 1360 cm⁻¹.Generally, the bulk graphite has a peak that belongs to the stretchingvibration mode of a C═C bond in the vicinity of 1580 cm⁻¹ (G band, peakintensity I₁₅₈₀). When disturbance occurs in the graphite structure, apeak in the vicinity of 1360 cm⁻¹ (D band, peak intensity I₁₃₆₀) isobserved. The carbon nanotubes of the present embodiment arecharacterized by its large peak at I₁₃₆₀ (D band) and by its broad bandsat I₁₅₈₀ (G band) and I₁₃₆₀ (D band), and by shifting of I₁₅₈₀ (G band)to the high frequency side in the vicinity of 1600 cm⁻¹. This is thephenomenon that is observed when there is disturbance in the structureof graphite (monocrystal), i.e., lowering of crystallinity. Thus, thecarbon nanotubes of the present invention have the carbon network filmof graphite and has low crystallinity. Considering the TEM image of FIG.16, it is believed that this low crystallinity is due to the structureof graphite that is divided into micro areas. Table 1 summarizes theresult of FIG. 17 using the degree of graphitization I₁₃₆₀/I₁₆₀₀, whichindicates crystallinity. TABLE 1 VAPOR-PHASE CARBON DEPOSITIONTEMPERATURE I₁₃₆₀/I₁₆₀₀ 600° C. 0.863 700° C. 0.800 800° C. 0.867 850°C. 0.866

[0208] Table 1 indicates degrees of graphitization of the carbonnanotube sample for structural analysis at vapor-phase carbon depositiontemperatures 600° C., 700° C., and 800° C. The degree of graphitizationof the carbon nanotube of the present invention was 0.5 to 1, and thatof the present embodiment in particular was around 0.8 to 0.9.

[0209]FIG. 18 and FIG. 19 are measurement results of X-ray diffraction(XRD) spectra with respect to the carbon nanotube sample for structuralanalysis, that were obtained by completely removing the anodic aluminumoxide film and by making the carbon nanotubes into a powder, as with thesample used for the TEM observation of FIG. 16. FIG. 18 shows themeasured X-ray diffraction (XRD) spectrum with 2θ in the range of 0° to50°, and FIG. 19 shows the measured X-ray diffraction (XRD) spectrumwith 2θ in the range of 40° to 50°, respectively showing data thatenable the crystallite size in the thickness direction and planedirection to be calculated. As FIG. 18 indicates, a sharp peak existsnear 2θ=25°. The peak enables the plane interval (d(002)) of thegraphite to be calculated. From FIG. 18 and the Bragg's equation, theplane interval (d(002)) of the carbon nanotubes of the presentembodiment can be calculated. Table 2 shows plane intervals (d(002)) ofthe carbon nanotubes when the vapor-phase carbon deposition temperatureswere 600° C., 700° C., and 800° C. TABLE 2 VAPOR-PHASE CARBON DEPOSITIONTEMPERATURE PLANE INTERVAL (d(002)) 600° C. 0.3915 nm 700° C. 0.3883 nm800° C. 0.3596 nm

[0210] The plane intervals of the carbon nanotubes were approximatelyfrom 0.34 nm to 0.40 nm. The plane interval (d(002)) of the graphite wasabout 0.3354 nm. The plane intervals of the carbon nanotubes were thussignificantly larger than the place interval of the graphite.

[0211] The apparent size of the crystallite can be calculated from theScherrer's equation. The peak of the X-ray diffraction (XRD) spectrumnear 2θ=25° indicates a (002) plane and that near 2θ=45° indicates a(10) plane. These can be used to calculate the crystallite size Lc (FIG.18) in the thickness direction (direction perpendicular to the tubeaxis) of the carbon network film and the crystallite size La (FIG. 19)in the plane direction (direction parallel to the tube axis) of thecarbon network film. Table 3 shows Lc of the carbon nanotubes when thevapor-phase carbon deposition temperatures were 600° C., 700° C., and800° C. Table 4 shows La of the carbon nanotubes when the vapor-phasecarbon deposition temperatures were 600° C., 700° C., and 800° C. TABLE3 VAPOR-PHASE CARBON CRYSTALLITE SIZE (Lc) IN DEPOSITION TEMPERATURETHICKNESS DIRECTION 600° C. 1.26 nm 700° C. 1.55 nm 800° C. 1.89 nm

[0212] TABLE 4 VAPOR-PHASE CARBON CRYSTALLITE SIZE (La) IN DEPOSITIONTEMPERATURE PLANE DIRECTION 600° C. 3.20 nm 700° C. 3.99 nm 800° C. 5.26nm

[0213] The Lc of the carbon nanotubes of the present embodiment was 1 nmto 2 nm, and La was 3 nm to 6 nm. One can understand that these aresignificantly smaller than the crystallite size of graphite that rangesfrom several mm to several cm. It can be seen from the measurementresults of these X-ray diffraction (XRD) spectra that the size of themicro areas of the carbon nanotubes of the present embodiment is 3 nm to6 nm. It can also be seen from FIG. 16 that the carbon nanotubes have adiameter of about 26 nm. Thus, it can be seen that the carbon networkfilm of the carbon nanotubes of the present embodiment is divided intomicro areas which are smaller in size than the diameter of the carbonnetwork film. The measurement results of the X-ray diffraction (XRD)spectra also made it clear that the micro areas of the carbon nanotubesof the present invention have a size of about several nm. The size ofthe carbon nanotubes along the tube axis direction is several tens ofμm, and it thus can be seen that the carbon network film is divided intolarge numbers of areas in the tube axis direction.

[0214] The result of Raman spectrometry and the measurement result ofthe X-ray diffraction (XRD) spectra indicate low crystallinity(polycrystallinity, not monocrystal) of the carbon nanotubes of thepresent invention. A metal coating (platinum coating) was applied on theboth sides of the carbon nanotube sample for structural analysis, and abias was applied onto these surfaces so as to measure resistance. Theresult of measurement showed that the carbon nanotubes of the presentinvention had a resistivity of about 1 kΩ·cm to about 100 kΩ·cm. This isconsiderably higher than the resistance of conventional carbon nanotubes(carbon nanotubes that are synthesized by arc discharge) of about 5×10⁻⁴kΩ·cm. Thus, the carbon nanotubes of the present invention can becharacterized to have low crystallinity also by electrical evaluation.Note that, in order to further reduce field emission current, carbonnanotubes with a resistivity of 50 kΩ·cm to 70 kΩ·cm was most suitable.

[0215] It was confirmed that such a structure of the low crystallinitycarbon nanotubes was preferable in reducing the emission start voltageand the driving voltage. In conventional electron source structures, ahigh resistor layer was provided under the electron source. The electronsource of the present invention does not require an additional highresistor layer because of a high resistivity of the carbon nanotubesitself, that is in a range of about 1 kΩ·cm to 100 kΩ·cm.

[0216] [Fourth Embodiment]

[0217] The present embodiment explains electrical characteristics, i.e.,field emission characteristics of the carbon nanotubes of the presentinvention.

[0218] Carbon nanotubes were prepared as in the Third Embodiment andfield emission characteristics of the bipolar tube structure wereevaluated. FIG. 20 shows a field emission characteristics evaluationdevice of a carbon nanotube electron source of the present embodiment;FIG. 21 shows emission current-applied voltage characteristics (“I-Vcharacteristics” hereinafter) of the carbon nanotube electron source ofthe present embodiment, and FIG. 22 is a Fowler-Nordheim plot of thecarbon nanotube electron source of the present embodiment (R. H. Fowlerand L. W. Nordheim, Proc. R. Soc. London, Ser. A119, 173 (1928)).

[0219] The carbon nanotube electron source of the present embodiment wasprepared by detaching the anodic aluminum oxide film that is formed onthe aluminum substrate, followed by vapor-phase carbon deposition (2.5%propylene in nitrogen, 800° C., 3 hours), as explained in the ThirdEmbodiment. The anodic aluminum oxide film after vapor-phase carbondeposition was subjected to the oxygen plasma process (500 W, oxygenflow rate of 100 sccm, 10 Pa, 10 minutes) by reactive ion etching, so asto remove the carbon deposition film on the surface of the anodicaluminum oxide film. The anodic aluminum oxide film was removed by wetetching (20% sodium hydroxide aqueous solution, 150° C., 2 hours). Thefield emission characteristics evaluation device shown in FIG. 20 wasused to evaluate field emission characteristics of the carbon nanotubeelectron source thus obtained. Referring to FIG. 20, the carbon nanotubeelectron source (carbon nanotube array in which a plurality of carbonnanatubes 8 are bound by the alumina particles) was bonded (anchored) onthe cathode electrode wiring 2 (conductive substrate) using a conductivepaste such as a silver paste or a carbon paste, so as to provide acathode electrode that is provided with the carbon nanotubes. Note that,as the substrate for supporting the carbon nanotube electron source, aninsulating substrate such as a glass substrate may be provided insteadof the conductive substrate. In this case, the conductive paste can alsoserve as the cathode electrode wiring 2.

[0220] An anode electrode 27 is provided opposite the cathode electrodewith the carbon nanotubes (cathode electrode wiring 2 and carbonnanatubes 8), and a spacer was inserted between the cathode electrodewith the carbon nanotubes and the anode electrode 27, so as to form anelectrode gap. In the field emission characteristics evaluation, theelectrode gap was the distance between the tips of the carbon nanatubes8 and the anode electrode 27. In the present embodiment, the electrodegap was 2 mm, and a driving voltage was applied between the anodeelectrode 27 and the cathode electrode wiring 2, so as to measure fieldemission current density. FIG. 21 shows I-V characteristics of fieldemission current of the carbon nanotube electron source of the presentembodiment. Field emission of the carbon nanotube electron source of thepresent embodiment started when the intensity of the driving electricfield was 0.25 V/μm, and at the intensity of the driving electric field1 V/μm, a field emission current density at or greater than 10 mA/cm²(about 10.5 mA/cm²) was observed.

[0221] Table 5 shows field emission start electric field intensity andoperating electric field intensity (driving electric field intensitythat is required to generate a field emission current of 10 mA/cm²current density) for the carbon nanotube electron source (PresentEmbodiment) of the present embodiment, a carbon nanotube electron source(Comparative Example 1) that was made by a conventional arc dischargetechnique, and a conventional Spindt type metal electron source(Comparative Example 2). Note that, the field emission start electricfield intensity was determined from the graph of I-V characteristics.The field emission current that is generated when an electric field withthe field emission start electric field intensity was applied is at thelevel of less than several tens of nA/cm². The field emission currentrequired for a typical high voltage thin film image forming device canbe designed with the field emission current density of about 10 mA/cm².TABLE 5 OPERATING FIELD EMISSION ELECTRIC FIELD START ELECTRIC INTENSITYFIELD INTENSITY (10 mA/cm²) PRESENT 0.25 V/μm 1 V/μm EMBODIMENTCOMPARATIVE 10 V/μm 25 V/μm EXAMPLE 1 COMPARTIVE 100 V/μm 140 V/μmEXAMPLE 2

[0222] Note that, the carbon nanotube electron source of ComparativeExample 1 was prepared by a method in which the carbon nanotubes made byarc discharge were dispersed in ethanol and then anchored on atetrafluoroethylene resin (product name “Teflon” provided by Du Pont)plate (W. A. de Heer et al., Science, 270, 1179 (1995)).

[0223] The field emission characteristics of the carbon nanotubes ofComparative Example 1 were measured as follows. First, a grid electrodewas disposed on the carbon nanotube electron source of ComparativeExample 1 so that a gap of 20 μm from the carbon nanotubes was provided.A voltage was applied between the grid electrode and the carbonnanotubes and the voltage was gradually increased so as to measure I-Vcharacteristics. FIG. 40 shows the result of measurement. It can be seenfrom the graph of I-V characteristics of FIG. 40 that field emissionstarts when the electric field intensity reaches 10 V/μm (when theapplied voltage reaches 200 V).

[0224] Note that, the carbon nanotube electron source of ComparativeExample 1 is described as oriented carbon nanotubes in the document “W.A. de Heer et al., Science, 270, 1179 (1995)”. However, the carbonnanotube electron source of Comparative Example 1 is actually a castfilm (a film of carbon nanotubes whose tips (tube axes) direct not in adirection exactly perpendicular to the substrate but in otherdirections). It is therefore assumed that the carbon nanotube electronsource of Comparative Example 1 has an inferior carbon nanotubeorientation state than that of the carbon nanotube electron source ofthe present embodiment. The carbon nanotube electron source of thepresent embodiment differs from the carbon nanotube electron source ofComparative Example 1 in which individual pieces of carbon nanotubes areoriented. In the carbon nanotube electron source of the presentembodiment, the carbon nanotubes are bound to one another by the fineparticles of the anodic aluminum oxide film and the carbon nanotubes donot exist in separate pieces. Thus, a desirable orientation state (theaxis direction of the carbon nanotubes is oriented in a directionperpendicular to the substrate) is maintained. The orientation state ofthe carbon nanotubes of the present embodiment is therefore far moresuperior than that of Comparative Example 1.

[0225] As is clear from Table 5, the field emission start electric fieldintensity of the carbon nanotube electron source of the presentembodiment is 0.25 V/μm and is notably small, which is about {fraction(1/40)} of that (10 V/μm) of the conventional carbon nanotube electronsource (Comparative Example 1), and about {fraction (1/400)} of that(100 V/μm) of the conventional metal electron source (ComparativeExample 2). The operating electric field intensity (driving electricfield intensity that is required to generate a field emission current of10 mA/cm² current density) of the carbon nanotube electron source of thepresent embodiment is 1 V/μm, which is a significant drop to about{fraction (1/25)} of that (25 V/μm) of the conventional carbon nanotubeelectron source (Comparative Example 1), and about {fraction (1/140)} ofthat (140 V/μm) of the conventional metal electron source (ComparativeExample 2). The carbon nanotube electron source of the present inventioncapable of low-voltage driving allows use of a conventional thin-filmtransistor (TFT) that is driven in a voltage range of about 20 V to 30V, which enables the carbon nanotube electron source of the presentinvention to be installed in displays such as a field emission display.From a different perspective, in the carbon nanotube electron source ofthe present embodiment, the field emission current density when anelectric field of 1 V/μm electric field intensity is applied is 10mA/cm², which is higher than that of conventional carbon nanotubeelectron sources.

[0226] Note that, it is envisaged that the field emission start electricfield intensity and the operating electric field intensity become weakwhen the density of the carbon nanotubes is reduced and the electricfield is concentrated, as in the carbon nanotube electron source of theJapanese Patent Publication for Unexamined Patent Application No.57934/2000 (Tokukai 2000-57934). It is therefore required that the fieldemission start electric field intensity and the operating electric fieldintensity be compared at the same density. The result of Table 5 is theresult of measurement at a relatively high carbon nanotube density.

[0227]FIG. 22 is a Fowler-Nordheim plot of the I-V characteristics ofFIG. 21. Typically, field emission characteristics are expressed byFowler-Nordheim relations (R. H. Fowler and L. W. Nordheim, Proc. R.Soc. London, Ser. A119, 173 (1928)), and in a plot where the verticalaxis represents 1/Va and the horizontal axis represents log (Ia/Va²)(Ia: emission current, Va: applied voltage), the Fowler-Nordheim plot islinear, ascending to the left. FIG. 22 clearly indicates that theFowler-Nordheim of the carbon nanotube electron source of the presentembodiment has a good linear relationship, and it was confirmed that theI-V characteristics of the carbon nanotube electron source of thepresent embodiment as shown in FIG. 21 is the field emissioncharacteristics.

[0228] [Fifth Embodiment]

[0229] The present embodiment describes a structure of carbon nanotubes(surface modified carbon nanotubes) that are obtained by performingsurface modification in a field emission area of the carbon nanotubes ofthe present invention, and field emission characteristics of such carbonnanotubes, with reference to the SEM images of FIG. 23 through FIG. 30,the field emission characteristics (I-V characteristics) of FIG. 31, andthe results of surface analysis (results of measurement on X-rayphotoelectron spectrometry (XPS) spectrum) shown in FIG. 32 through FIG.35. The surface modified carbon nanotubes emit electrons at a lowervoltage than the carbon nanotubes before the surface modification.

[0230]FIG. 23 and FIG. 24 are SEM images of carbon nanotubes after anoxygen (O₂) plasma process (etching with oxygen plasma), in which FIG.23 is the SEM image viewed diagonally from above on a 45° angle; andFIG. 24 is the SEM image viewed top down. FIG. 25 and FIG. 26 are SEMimages of carbon nanotubes after a CHF₃ plasma process (etching withCHF₃ plasma), in which FIG. 25 is the SEM image viewed diagonally fromabove on a 45° angle; and FIG. 26 is the SEM image viewed top down. FIG.27 and FIG. 28 are SEM images of carbon nanotubes after an Ar plasmaprocess (etching with Ar plasma), in which FIG. 27 is the SEM imageviewed diagonally from above on a 45° angle; and FIG. 28 is the SEMimage viewed top down. FIG. 29 and FIG. 30 are SEM images of (untreated)carbon nanotubes without a plasma process, in which FIG. 29 is the SEMimage viewed diagonally from above on a 45° angle; and FIG. 30 is theSEM image viewed top down. Note that, as the term is used herein,“diagonally from above on a 45° angle” and “top down” are with respectto the carbon nanotubes that are disposed with their exposed end surfacefacing up and with respect to the base substrate that is disposedhorizontally, as shown in FIG. 7.

[0231]FIG. 31 shows field emission current-applied voltagecharacteristics of the carbon nanotube electron source after the O₂plasma process, of the carbon nanotube electron source after the CHF₃plasma process, of the carbon nanotube electron source after the Arplasma process, and of the untreated carbon nanotube electron source.FIG. 32 shows the result of measurement on X-ray photoelectronspectrometry (XPS) spectrum of the carbon nanotubes after the O₂ plasmaprocess.

[0232] In the present embodiment, the anodic aluminum oxide film formedon the aluminum substrate was detached and subjected to vapor-phasecarbon deposition (2.5% propylene in nitrogen, 800° C., 3 hours), as inthe Third Embodiment. The anodic aluminum oxide film after thevapor-phase carbon deposition was subjected to a plasma process byreactive ion etching (RIE), so as to. remove the carbon deposition filmon the surface of the anodic aluminum oxide film. The anodic aluminumoxide film was removed by wet etching (20 weight % sodium hydroxideaqueous solution, 150° C., 2 hours). In the present embodiment, variousplasma processes (O₂ plasma process, CHF₃ plasma process, and Ar plasmaprocess) were carried out to confirm the structure and field emissioncharacteristics.

[0233] In the present embodiment, the plasma processes employed sputteretching. The sputter etching is a technique in which plasma is generatedon a sample position and an electric field is applied to the sample, soas to cause bombardment of ions in the plasma on the sample. Amongdifferent types of sputter etching, those with a chemical reactionmechanism in which active ions are reacting species are called reactiveion etching (RIE). Among the foregoing three types of plasma processes,the O₂ plasma process and CHF₃ plasma process are reactive ion etching,and the Ar plasma process is physical sputter etching.

[0234] In the carbon nanotubes after the O₂ plasma process, as shown bythe SEM images of FIG. 23 and FIG. 24, multi-walls on the end surface ofthe carbon nanotubes (surface modified area, the cross section at thetop of the carbon nanotubes) can be clearly observed, thereby confirmingthe hollow structure.

[0235] In the carbon nanotubes after the CHF₃ plasma process, as clearlyindicated in FIG. 25 and FIG. 26, the hollow structure of the carbonnanotubes cannot be observed. Rather, the end surface of the carbonnanotubes appears to be closed.

[0236] Further, as shown in FIG. 27 and FIG. 28, the wall was alsoobserved on the end surface of the carbon nanotubes after the Ar plasmaprocess, though not as clearly as that of the carbon nanotubes after theO₂ plasma process.

[0237] For comparison, SEM images of the carbon nanotubes untreated bythe plasma process are shown in FIG. 29 and FIG. 30. It can be seen thatthe carbon deposition film adheres on the surface of the anodic aluminumoxide film. Particularly, as can be seen in FIG. 30 which shows theanodic aluminum oxide film as viewed directly from above, the carbondeposition film adheres to the extent where the pores of the anodicaluminum oxide film are buried.

[0238] Note that, the plasma process, as it is used in the producingprocess, is performed to remove the carbon (surface carbon) that hasdeposited on the surface of the anodic aluminum oxide film, so as toshape the carbon nanotubes. That is, without the plasma process, thecarbon that has deposited on the surface of the anodic aluminum oxidefilm is not removed and the independent shapes of the carbon nanotubescannot be obtained. In other words, the carbon nanotubes without theplasma process do not have the independent shapes.

[0239] The O₂ plasma process and the CHF₃ plasma process of the presentembodiment are chemical etching in which oxygen radicals in the case ofthe former and fluorine radicals in the case of the latter react withcarbon to proceed etching. On the other hand, the Ar plasma process isphysical etching in which Ar⁺ ions, which are inert ions, are sputteredto proceed etching. It is envisaged that the sharp end surface of thecarbon nanotubes processed by O₂ plasma is due to oxidation of thecarbon that makes up the tips of the carbon nanotubes and removal of theoxidized carbon in the form of a gas as a result of the O₂ plasmaprocess. It is believed that the reason the end surface of the carbonnanotubes processed by CHF₃ plasma appears to be closed is that thecarbon that makes up the tips of the carbon nanotubes reacts withfluorine radicals, and fluorides (fluorocarbon) are deposited on thetips (end surface) of the carbon nanotubes. On the other hand, the endsurface of the carbon nanotubes processed by Ar plasma is physicallysputtered by Ar ions and thus believed to have some irregularities asshown in FIG. 28. It is envisaged that dangling bonds exist in highdensity in the end surface.

[0240]FIG. 31 shows field emission characteristics (I-V characteristics;plotted by ∘) of the carbon nanotubes processed by O₂ plasma, fieldemission characteristics (I-V characteristics; plotted by Δ) of thecarbon nanotubes processed by CHF₃ plasma, and field emissioncharacteristics (I-V characteristics; plotted by □) of the carbonnanotubes processed by Ar plasma. Note that, at an electric fieldintensity at or below 5 V/μm, field emission was not observed in thecarbon nanotubes not processed by the plasma process. As is clear fromFIG. 31, the field emission start electric field intensities of thecarbon nanotubes were 0.25 V/μm, 1.25 V/μm, and 3.0 V/μm in the O₂plasma process (∘ plot), the CHF₃ plasma process (Δ plot), and the Arplasma process (□ plot), respectively. Thus, it was found that the fieldemission start electric field intensity of the carbon nanotubes waslowest in the O₂ plasma process (∘ plot), followed by the CHF₃ plasmaprocess (Δ plot) (about 5 times greater than the O₂ plasma process) andthe Ar plasma process (□ plot) (about 12 times greater than the O₂plasma process). Note that, the field emission start electric fieldintensity of the carbon nanotubes processed by Ar plasma is about ⅓ ofthat of conventional carbon nanotubes, which is sufficiently low.

[0241]FIG. 32 through FIG. 35 are X-ray photoelectron spectrometry(hereinafter “XPS”) spectra. Shown in FIG. 32 through FIG. 34 aremeasurement data of carbon nanotubes that are processed by O₂ plasma,CHF₃ plasma, and Ar plasma. Shown in FIG. 35 is measurement data of thecarbon nanotubes before the plasma process (unprocessed by the plasmaprocess). In the spectrum of the carbon nanotubes not processed by theplasma process as shown in FIG. 35, a sharp peak (C1s) that derives fromthe graphite structure forming hybrid sp² orbitals is observed at 284.6eV. By comparing the plasma processed carbon nanotubes (FIG. 32 throughFIG. 34) with the unprocessed carbon nanotubes (FIG. 35), it can be seenthat the peaks of the plasma processed carbon nanotubes are broader thanthe peak of the unprocessed carbon nanotubes. Further, the XPS spectraof the carbon nanotubes processed by O₂ plasma (FIG. 32), CHF₃ plasma(FIG. 33), and Ar plasma (FIG. 34) have shoulder peaks in the vicinityof 290 eV. Further, the XPS spectra of the carbon nanotubes processed byO₂ plasma (FIG. 32) and CHF₃ plasma (FIG. 33) have large peaks in thevicinity of 286 eV. The peak in the vicinity of 286 eV can be attributedto the C—O bonds, and the peak in the vicinity of 290 eV can beattributed to the O═C—O bonds. The XPS spectrum of the carbon nanotubesprocessed by O₂ plasma has a broad peak shape (peak area) in a domain of286 eV to 290 eV, and therefore it is envisaged that the covalent bondsthat connects oxygen and carbon in high concentration have in some wayinfluenced the low voltage field emission of the carbon nanotubeelectron source of the present invention. However, the composition ratio(O/C) of oxygen with respect to carbon in the field emission area of thecarbon nanotubes of the present embodiment, that was found from the XPSspectra of FIG. 32 through FIG. 34, was around 0.1 to 0.3. Further, thepeak in the vicinity of C1s (286.6 eV) was broader in order of no plasmaprocess (half bandwidth of the 284.6 eV peak: 2.2 eV), the Ar plasmaprocess (half bandwidth of the 284.6 eV peak: 3.0 eV), the CHF₃ plasmaprocess (half bandwidth of the 284.6 eV peak: 3.0 eV), and the O₂ plasmaprocess (half bandwidth of the 284.6 eV peak: 4.2 eV). It is envisagedfrom these X-ray diffraction (XRD) spectra that the oxygen connected tocarbon has some influence on field emission. Also, the bonding state ofcarbon and oxygen may be related to field emission in some way.

[0242] Note that, the foregoing plasma processes may be plasma etchingin which plasma of an active gas such as O₂ or CHF₃ is generated on asample position so as to cause radials in the plasma to react with thesample, or reactive ion beam etching in which an ion beam of active ionsgenerated from an active gas such as O₂ or CHF₃ is projected on asurface of the sample. Further, the plasma processes may be physical ionbeam etching in which an ion beam of inert ions generated from an inertgas such as Ar is projected on a surface of the sample.

[0243] [Sixth Embodiment]

[0244] Referring to FIG. 36 and FIG. 37, the following explains a fieldemission display (FED) in which the carbon nanotube electron source ofthe present invention is installed in a field emission part (pixel).

[0245] A plurality of cathode electrode wires 2 that are parallel to oneanother are formed on a base substrate 1 made of an insulating materialsuch as a glass substrate or a ceramic substrate. On the cathodeelectrode wires 2 are formed an anodic oxidation stopping layer (highresistor layer) 3. The anodic oxidation stopping layer (high resistorlayer) serves to limit the field emission current, and is made ofsilicon, silicon carbide, silicon oxide, silicon nitride, or a mixtureof these compounds. On the anodic oxidation stopping layer (highresistor layer) 3 and the cathode electrode wires 2 are formed the fieldemission part, i.e., pixels, and the carbon nanatubes 8 are formed onthe pixels. The carbon nanatubes 8 are anchored by the anodic aluminumoxide film 5. The anodic aluminum oxide film 5 is shown flat in FIG. 36,but an alternate arrangement, in which the carbon nanatubes 8 areanchored by particles, is also possible. The FED tested in the presentembodiment is designed to have a 100 μm×100 μm pixel and to have about10⁶ carbon nanatubes 8. Around the pixels are formed the gate insulatinglayer 10, and the gate electrode wires 11 are formed on the gateinsulating layer 10 so as to be orthogonal to the cathode electrodewires 2. The pixels are XY addressed by the cathode electrode wires 2and the gate electrode wires 11. In the present embodiment, a singlegate opening of 100 μm×100 μm is provided to make up one pixel. However,a single pixel may be divided into a plurality of parts. For example,one hundred of 1 μm×1 μm gate openings may be provided to make up apixel. By thus dividing the pixel into micro areas, redundancy of fieldemission can be obtained.

[0246] Further, in the carbon nanotube electron source of the presentinvention, the carbon nanatubes 8 are provided such that each carbonnanotube 8 is provided for each of large numbers of pores of thetemplate (porous film). The template with large numbers of pores mustsatisfy the condition that the pore density is readily controlled. Inthe present invention, it is preferable that the template with largenumbers of pores is the porous anodic aluminum oxide film. Bycontrolling the pore density of the porous anodic aluminum oxide film todesign the density of the carbon nanotubes, the electric field of thecarbon nanotubes can be more concentrated and the efficiency of fieldemission can be improved (lower voltage is required for the fieldemission). The anodic aluminum oxide film 5 is described in more detailbelow. The anodic alumina oxide film 5 has an important role indesigning the shape of the carbon nanatubes 8. That is, the length,diameter, and density of the carbon nanotubes 8 are dependent on thethickness of the anodic aluminum oxide film 5 and the diameter anddensity of the pores 6 of the anodic aluminum oxide film 5,respectively. As the anodic aluminum oxide film 5, an aluminum, film 4that is formed by a sputtering method or a vapor deposition method isused, and the thickness of the anodic aluminum oxide film 5 iscontrolled. It was verified by experiment that the thickness of theanodic aluminum oxide film was about 1.5 times that of the aluminum film4. However, when 10 μm or thicker thickness is required for the anodicaluminum oxide film 5, it is preferable that the anodic aluminum oxidefilm 5 be made by pasting aluminum foils. The diameter and density ofthe pores of the anodic aluminum oxide film can be easily be controlledby a chemical solution of the anodic oxidation or by applied voltage,etc. By forming the anodic aluminum oxide film 5 according to the devicedesign and by using the corresponding carbon nanotubes as the electronsource, carbon nanatubes 8 with superior field emission characteristicscan be structured.

[0247] Further, the carbon nanotubes of the present invention cancontain a conductive material inside the tubes. By containing aconductive material inside the tubes, the resistance of the electronsource can be reduced and a carbon nanotube electron source capable ofemitting large current electrons can be realized. An organic metalmaterial such as iron can be readily introduced into the tubes in avapor phase. In the present embodiment, iron was contained in the carbonnanotubes using ferrocene, so as to reduce resistance of the carbonnanotube electron source. As a result, large current field emission ofaround several A/cm² was observed.

[0248] A back plate having the described cathode structure and a faceplate having a fluorescent material 28 on the anode electrodes 27 aredisposed opposite to each other with a gap of 1 mm to 2 mm therebetween.A voltage of around 5 kV to 7 kV was applied to the anode electrodes 27to cause the carbon nanotube electron source of the tripolar tubestructure to emit electrons toward the fluorescent material 28. As aresult, emission of light from the fluorescent material 28 was observedand the luminance of the light was 10,000 cd/m². Therefore, it wasconfirmed that the thin display having installed therein the carbonnanotube electron source of the present embodiment had superior devicecharacteristics that consumes low power and produces high luminance.

[0249] Note that, the carbon nanotube electron source disclosed inJapanese Publication for Unexamined Patent Application No. 10-12124 haslead electrodes (grid) at the openings of the pores of the anodicaluminum oxide film, and therefore has a problem that manufacturingyield is low and the driving pulse signal waveform is susceptible todegradation by the thin electrodes that cannot be made thicker.

[0250] In contrast, in the carbon nanotube electron source of thepresent embodiment, the gate electrode wires 11 are formed not over theopenings of the pores of the anodic aluminum oxide film 5 but in thevicinity of the openings of the pores of the anodic aluminum oxide film5, without covering the openings. This enables production yield to beimproved and the thickness of the electrodes to be increased, therebypreventing degradation of the driving pulse signal waveform.

[0251] The following explains a driving method of the electron sourcethat can emit electrons at a low voltage. The driving method is not justlimited to the carbon nanotube electron source of the present embodimentbut is also applicable to, for example, a diamond electron source thathas negative electron affinity.

[0252]FIG. 37 is a cross sectional view of the FED (display) of thepresent embodiment. The back plate (cathode side) includes the base(glass) substrate 1, the cathode electrode wiers 2, the anodic oxidationstopping layer 3 (high resistor layer), the carbon nanatubes 8, the gateinsulating layer 10, and the gate electrode wires 11. The gate electrodewires 11 extend into the plane of the paper in the drawing, and thecathode electrode wires 2 extend from the right toward the left of thedrawing. The face plate (anode side) is made up of the base substrate29, the anode electrode 27, which is a transparent electrode made ofindium tin oxide or the like, and the fluorescent material 28. The panelsize was diagonally 5 inches, the number of pixels was 320×240, and agetter was disposed with a degree of vacuum at 10⁻⁸ Torr.

[0253] In the FED (display) of the present embodiment, the cathodeelectrode wiers 2, the gate electrode wires 11, the anode electrode 27,and a power supply which applies a voltage to these elements make upelectric field applying means that applies an electric field to thecarbon nanatubes 8.

[0254] In the display using the carbon nanotube electron source of thepresent embodiment, the driving electric field intensity E_(A) betweenthe anode electrode 27 and the carbon nanatubes 8 is greater than thedriving electric field intensity E_(G) between the gate electrode wires11 and the carbon nanatubes 8. That is,

E _(A)=(V _(A) −V _(C))/G _(A) >E _(G)=(V _(G) −V _(C))/G _(G)

[0255] where V_(A) is the anode voltage, V_(G) is the gate voltage,V_(C) is the cathode voltage, G_(A) is the gap between the anodeelectrode 27 and the carbon nanatubes 8, and G_(G) is the gap betweenthe gate electrode wires 11 and the carbon nanatubes 8.

[0256] In the present embodiment, when the anode voltage V_(A) is 5 kV,the cathode voltage V_(C) is grounded, and the gap G_(A) between theanode electrode 27 and the carbon nanatubes 8 is 1 mm, E_(A)=5×10⁴ V/cm.

[0257] The carbon nanatubes 8 of the present embodiment was driven bythe driving method of the present embodiment. The fluorescent material28 on the face plate emitted light when the gate voltage V_(G)=0 V, andthe light from the fluorescent material 28 diminished when the gatevoltage V_(G) was increased (e.g., when the gap G_(G) between the gateelectrode wires 11 and the carbon nanatubes 8 was 6 μm, and the gatevoltage V_(G) was 30 V). This is because the decrease (OFF) of theelectric field intensity E_(G) between the gate electrode wires 11 andthe carbon nanatubes 8 reduces the field emission current. Driving ofthe display was enabled in this manner.

[0258] It was also confirmed by simulation that with the driving methodof the present embodiment, the emitted electron beam was able toconverge, making it possible to prevent crosstalk without providing aconverging electrode.

[0259] For example, a conventional carbon nanotube electron source withan emission start electric field intensity of several V/cm, when it isdesigned with essentially the same structure as that of the presentembodiment, would require a higher anode voltage V of several tens of kVor a smaller gap of several hundreds of μm, which is not practical.Further, the gate voltage V_(G) needs to be increased to severalhundreds of volt and a high resistant driver will be required.

[0260] The foregoing problem of the conventional carbon nanotubeelectron source can be solved effectively with the use of the lowvoltage driving carbon nanotube electron source of the presentembodiment as described above. The use of the carbon nanotube electronsource of the present embodiment not only enables the device to bedesigned with a resistant margin of applied voltage but also allows useof a low voltage driver such as a TFT driver, thus reducing cost of thedevice.

[0261] [Seventh Embodiment]

[0262] A carbon nanotube of the present embodiment partially hasamorphous areas in its structure, and is produced by a method asdescribed in the First Embodiment.

[0263] An SEM observed image has shown that the carbon nanotube of thepresent embodiment has a diameter of 30 nm and a length of 75 μm. TheSEM observed image has also shown that the carbon nanotube of thepresent embodiment had superior orientation and notably high density.Further, the carbon nanotube of the present embodiment, because it isformed by using pores with open ends as a template, contained onlycarbon atoms without a metal catalyst or the like.

[0264] Characteristics of conventional carbon nanotubes are explainedbelow. Conventional carbon nanotubes are formed by an arc dischargemethod or a CVD method using a metal catalyst such as cobalt, iron, ornickel. Conventional carbon nanotubes formed by arc discharge had aclosed end and non-uniform diameter and length. Further, conventionalcarbon nanotubes formed by a CVD method, because they had a closedgrowth end and used a metal catalyst such as cobalt, iron, or nickel,contained a catalyst metal as constituting atoms. Detailed descriptionof a growth model of such a carbon fiber using catalyst metal has beengiven by Endo et al. (Morinobu, ENDO, Solid State Physics, 12, 1(1977)).

[0265] The biggest difference in the shape of the carbon nanotubes ofthe present embodiment and that of the conventional carbon nanotubes isthe presence or absence of micro crystal defects (amorphous areas) inthe carbon nanotubes. The inventors of the present invention have provenby experiment that this difference has the largest influence on fieldemission characteristics such as the field emission start voltage anddriving voltage.

[0266] The carbon nanotube of the present embodiment partially has microcrystal defects (amorphous areas), which appear as “joints” under TEM.In the carbon nanotube of the present embodiment, a graphite layerobserved under TEM extends in the lengthwise direction of the tube andis divided into micro areas and is discontinuous (intermittent). Thischaracteristic structure of the carbon nanotubes of the presentembodiment is obtained by the carbonization reaction that takes place onthe inner wall of the template (porous alumina) without using a metalcatalyst for the growth of the carbon nanotubes. The carbon nanotubes ofthe present embodiment are the result of carbonization on the inner wallof the pores of the template, and the carbon nanotubes grow as theyimpart a huge stress on the inner wall of the pores. It is believed thatthe discontinuous graphite structure is the result of the influence ofsuch a stress on graphite layer formation.

[0267] On the other hand, the conventional carbon nanotubes that areformed by arc discharge, as shown by the TEM observed image in thepublication Y. Saito, Ultramicroscopy, 73, 1(1998)), do not have the“joints” associated with the amorphous areas observed in the presentembodiment. Rather, the graphite layer is continuously formed in thelengthwise direction of the tubes.

[0268] Note that, it is believed that the carbon nanotubes with theamorphous areas (crystal defects) can also be produced by causingcrystal defects to generate on carbon nanotubes that were formed by aconventional method using arc discharge or a method using a metalcatalyst, by bombardment of ions of an inert gas such as argon orhelium. However, the carbon nanotubes obtained in this manner may nothave the graphite areas (micro crystal areas) of equal interval alongthe lengthwise direction of the tubes as the carbon nanotubes of thepresent embodiment.

[0269] [Eighth Embodiment]

[0270] A carbon nanotube of the present embodiment partially hasamorphous areas in its structure, and is produced by a method asdescribed in the First Embodiment.

[0271]FIG. 40 compares a carbon nanotube electron source of the presentembodiment and the conventional carbon nanotube electron source of arcdischarge with respect to their field emission characteristics (I-Vcurve). It can be seen that the carbon nanotube electron source (∘ plotin the drawing) has a significantly lower field emission start voltagethan the conventional carbon nanotube electron source (broken line inthe drawing). It can also be seen that the carbon nanotube electronsource of the present embodiment has a steep rise of field emissioncurrent and the field emission current is obtained at a low drivingvoltage.

[0272] Note that, in the described embodiments, the vapor-phase carbondeposition method (pyrolysis of hydrogen carbide) was used to depositcarbon in the pores. However, the method of depositing carbon in thepores is not particularly limited and it is also possible to employ anarc discharge method in which arc discharge is induced between twocarbon electrodes to generate carbon vapor, or a laser vaporizationmethod in which a carbon rod is irradiated with a laser to generatecarbon vapor. Regardless of the arc discharge method or laservaporization method, the temperature in the growing space of the carbonnanotubes (not in the vicinity of the carbon rod but in the vicinity ofthe surface where the carbon deposition film is formed) is preferably600° C. to 900° C.

[0273] Further, the foregoing embodiments used the multi-walled carbonnanotubes. However, the present invention can also be realized bysingle-walled carbon nanotubes.

[0274] The invention being thus described in the specific embodiments orexamples in the best mode for carrying out the invention section, itwill be obvious that the same way may be varied in many ways. Suchvariations are not to be regarded as a departure from the spirit andscope of the invention, and all such modifications as would be obviousto one skilled in the art are intended to be included within the scopeof the following claims.

Industrial Applications of the Present Invention

[0275] As described, a carbon nanotube of the present invention has anarrangement in which a carbon network film has a polycrystal structurewhich is divided into a plurality of crystal areas in a tube axisdirection. In this way, a carbon nanotube that can emit large currentelectrons at a low voltage can be provided.

[0276] As described, an electron source of the present inventionincludes the carbon nanotube of the foregoing arrangement as a fieldemission part. In this way, an electron source that can emit largecurrent electrons at a low voltage can be provided.

[0277] A display of the present invention includes an electron sourcewhich has a plurality of carbon nanotubes of the foregoing arrangementas a field emission part, and electric field applying means for applyingan electric field to each carbon nanotube so as to cause each carbonnanotube to emit electrons. In this way, a display capable of carryingout low power display can be provided.

[0278] As described, a producing method of a carbon nanotube of thepresent invention is a method in which carbon is deposited in theabsence of a metal catalyst in the pores. In this way, a carbon nanotubethat can emit large current electrons at a low voltage can be provided.

[0279] As described, a producing method of an electron source of thepresent invention is a method in which a porous material with largenumbers of pores is used an a support member, and carbon is depositedinside the pores of the porous material in the absence of a metalcatalyst, so as to form a carbon deposition film of a cylindrical shape.In this way, an electron source that can emit large current electrons ata low voltage can be provided. Further, unlike a producing method thatuses a metal catalyst, there is no shape non-uniformity, which isdependent on the growth of the carbon nanotube, and therefore uniformityof field emission in the field emission area and the device plane can beimproved.

[0280] As described, a producing method of a carbon nanotube of thepresent invention is a method in which, a carbon deposition film, afterit is formed, is plasma etched so as to modify the field emission area.By thus modifying the field emission area, a carbon nanotube that canemit large current electrons at a low voltage can be provided.

[0281] As described, a producing method of an electron source of thepresent invention is a method in which a porous material with largenumbers of pores is used as a support member and carbon is depositedinside the pores of the porous material so as to form a carbondeposition film of a cylindrical shape, and thereafter the carbondeposition film is plasma etched to modify the tip of the carbondeposition film. In this way, the field emission area of the carbonnanotube can be modified, and thereby provide an electron source thatcan emit large current electrons at a low voltage.

[0282] As described, the electron source and display of the presentinvention have an arrangement that further includes particles, dispersedbetween carbon nanotubes, that bind side surfaces of the carbonnanotubes adjacent to one another. In this way, the electric fieldconcentrates on the carbon nanotubes more easily. As a result, it ispossible to provide an electron source that can emit large currentelectrons at a low voltage and a display capable of carrying out lowpower display.

[0283] As described, the electron source and display of the presentinvention have an arrangement in which the support member is a porouslayer, formed on a substrate, having large numbers of through-pores, andthe carbon nanotube is formed in a cylindrical shape inside the pores sothat one end of the carbon nanotube is closed on the side of thesubstrate and an end face of the carbon nanotube on the side of thesubstrate adheres to a surface of the substrate. As a result, anelectron source and a display with the carbon nanotubes firmly adheringto the support member can be realized with highly reliable electricalconnections between the carbon nanotubes and the support member.

[0284] As described, the electron source and display of the presentinvention have an arrangement in which the carbon nanotube is at leastpartially connected to the inner wall of the pores. In this way, thebond strength between the carbon nanotube and the support member can beincreased and the electron source and display can be realized with highreliability.

[0285] As described, the electron source and display of the presentinvention have an arrangement in which the emission start electric fieldintensity is in a range of from 0.25 V/μm to 0.5 V/μm. In this way, itis possible to provide an electron source that can emit large currentelectrons at a low voltage and a display capable of low power display.

[0286] As described, the electron source and display of the presentinvention have an arrangement in which an emission current density inresponse to an applied electric field intensity of 1 V/μm is in a rangeof 10 mA/cm² to 100 mA/cm². In this way, it is possible to provide anelectron source that can emit large current electrons at a low voltageand a display capable of low power display.

[0287] As described, a producing method of an electron source of thepresent invention includes the steps of forming on a base substrate ananodic oxidation stopping layer for stopping anodic oxidation of thebase substrate, prior to the anodic oxidation step of the base layer. Inthis way, an electron source with superior uniformity of emissioncharacteristics in the device plane or field emission area (pixels) canbe provided.

[0288] As described, the electron source of the present invention has anarrangement in which the carbon nanotube partially has an amorphous areain its structure. Further, the electron source of the present inventionhas an arrangement in which the carbon nanotube is discontinuousgraphite that is divided into micro areas in the tube axis direction.With these arrangements, the emission start voltage and operatingvoltage (device driving voltage) can be reduced.

[0289] As described, a producing method of an electron source of thepresent invention includes the steps of: forming a cathode electrodewiring on a substrate; forming a high resistor layer on the cathodeelectrode wiring; forming an inorganic material thin film in a fieldemission area on the high resistor layer; forming pores through theinorganic material thin film; disposing the carbon nanotube inside thepores; and modifying a surface of the carbon nanotube. By modifying thesurface of the field emission area according to this method, a lowvoltage driving electron source can be provided.

[0290] As described, the electron source of the present invention canemit large current electrons at a low voltage. This enables a TFT driverthat is used in conventional devices such as a liquid crystal device tobe used, thereby providing an ultralow power consuming and ultrahighluminance display.

What is claimed is:
 1. A carbon nanotube comprising at least one layerof a cylindrical carbon network film, wherein the carbon network filmhas a polycrystal structure which is divided into a plurality of crystalareas in a tube axis direction.
 2. The carbon nanotube as set forth inclaim 1, wherein a length of each crystal area in the tube axisdirection is in a range of from 3 nm to 6 nm.
 3. An electron sourcecomprising a carbon nanotube as a field emission part, wherein: thecarbon nanotube is at least one layer of a cylindrical carbon networkfilm, and carbon network film has a polycrystal structure which isdivided into a plurality of crystal areas in a tube axis direction. 4.The electron source as set forth in claim 3, wherein a length of eachcrystal area in the tube axis direction is in a range of from 3 nm to 6nm.
 5. A display comprising: an electron source which includes aplurality of carbon nanotubes as a field emission part; and electricfield applying means for applying an electric field to each carbonnanotube so as to cause each carbon nanotube to emit electrons, wherein:each carbon nanotube is at least one layer of a cylindrical carbonnetwork film, and the carbon network film has a polycrystal structurewhich is divided into a plurality of crystal areas in a tube axisdirection.
 6. A producing method of a carbon nanotube, comprising thestep of: depositing carbon inside large numbers of pores of a porousmaterial so as to form a carbon deposition film of a cylindrical shape,wherein the carbon is deposited in the absence of a metal catalyst inthe pores.
 7. The method as set forth in claim 6, further comprising: ananodic oxidation step for obtaining the porous material; and a heatingstep of not less than 600° C. after the anodic oxidation step.
 8. Themethod as set forth in claim 6 or 7, wherein the carbon is deposited byvapor phase carbon deposition in which gaseous hydrocarbon is carbonizedby pyrolysis.
 9. The method as set forth in claim 6 or 7, wherein a tipof the carbon deposition film is modified by plasma etching.
 10. Aproducing method of an electron source which includes a carbon nanotubeas a field emission part, and a support member for supporting the carbonnanotube, said method comprising the steps of: forming the supportmember using a porous material with large numbers of pores; anddepositing carbon in the pores of the porous material in the absence ofa metal catalyst in the pores, so as to form a carbon deposition film ofa cylindrical shape.
 11. The method as set forth in claim 10, furthercomprising: an anodic oxidation step for obtaining the porous material;and a heating step of not less than 600° C. after the anodic oxidationstep.
 12. The method as set forth in claim 10 or 11, wherein the carbonis deposited by vapor-phase carbon deposition in which gaseoushydrocarbon is carbonized by pyrolysis.
 13. The method as set forth inclaim 10 or 11, wherein a tip of the carbon deposition film is modifiedby plasma etching.
 14. A producing method of a carbon nanotube,comprising the step of: depositing carbon in large numbers of pores of aporous material so as to form a carbon deposition film of a cylindricalshape, wherein a tip of the carbon deposition film is modified by plasmaetching the carbon deposition film after forming the carbon depositionfilm.
 15. A producing method of an electron source which includes acarbon nanotube as a field emission part, and a support member forsupporting the carbon nanotube, said method comprising the steps of:forming the support member using a porous material with large numbers ofpores; and forming a carbon deposition film of a cylindrical shape bydepositing carbon in the pores of the porous material, and plasmaetching the carbon deposition film so as to modify a tip of the carbondeposition film.
 16. The method as set forth in claim 15, wherein oxygenplasma is used for the etching.
 17. An electron source comprising aplurality of carbon nanotubes that are disposed parallel to one anotheras a field emission part, said electron source further comprising:particles, dispersed between the carbon nanotubes, that bind sidesurfaces of the carbon nanotubes adjacent to one another.
 18. Theelectron source as set forth in claim 17, wherein the particles areγ-alumina.
 19. A display comprising: an electron source which includes aplurality of carbon nanotubes as a field emission part; and electricfield applying means for applying an electric field to each carbonnanotube so as to cause each carbon nanotube to emit electrons, saiddisplay further comprising: particles, dispersed between the carbonnanotubes, that bind side surfaces of the carbon nanotubes adjacent toone another.
 20. An electron source comprising a carbon nanotube as afield emission part and a support member for supporting the carbonnanotube, wherein: the support member is a porous layer, formed on asubstrate, having large numbers of through-pores, and the carbonnanotube is formed in a cylindrical shape inside the pores so that oneend of the carbon nanotube is closed on the side of the substrate and anend face of the carbon nanotube on the side of the substrate adheres toa surface of the substrate.
 21. The electron source as set forth inclaim 20, wherein the surface of the support member adhering to thecarbon nanotube is made of at least one kind of material selected fromthe group consisting of silicon, silicon carbide, silicon oxide, andsilicon nitride.
 22. A display comprising: an electron source, whichincludes a plurality of carbon nanotubes as a field emission part and asupport member for supporting each carbon nanotube; and electric fieldapplying means for applying an electric field to each carbon nanotube soas to cause each carbon nanotube to emit electrons, wherein: the supportmember is a porous layer, formed on a substrate, having large numbers ofthrough-pores, and each carbon nanotube is formed in a cylindrical shapeinside the pores so that one end of the carbon nanotube is closed on theside of the substrate and an end face of the carbon nanotube on the sideof the substrate adheres to a surface of the substrate.
 23. An electronsource comprising a carbon nanotube as a field emission part and asupport member for supporting the carbon nanotube, wherein: the supportmember is a porous material with large numbers of pores, and the carbonnanotube adheres at least partially to an inner wall of the pores.
 24. Adisplay comprising: an electron source, which includes a plurality ofcarbon nanotubes as a field emission part and a support member forsupporting each carbon nanotube; and electric field applying means forapplying an electric field to each carbon nanotube so as to cause eachcarbon nanotube to emit electrons, wherein: the support member is aporous material with large numbers of pores, and each carbon nanotube isbonded at least partially to an inner wall of the pores.
 25. A displaycomprising: an electron source, which includes a plurality of carbonnanotubes as a field emission part and a support member for supportingeach carbon nanotube; and electric field applying means for applying anelectric field to each carbon nanotube so as to cause each carbonnanotube to emit electrons, wherein: an emission start electric fieldintensity of the electron source is in a range of from 0.25 V/μm to 0.5V/μm.
 26. A display comprising: an electron source which includes aplurality of carbon nanotubes as a field emission part; and electricfield applying means for applying an electric field to each carbonnanotube so as to cause each carbon nanotube to emit electrons, whereinan emission current density of the electron source when an electricfield with an electric field intensity of 1 V/μm is applied is in arange of from 10 mA/cm² to 100 mA/cm².
 27. A producing method of anelectron source which includes a carbon nanotube as a field emissionpart and a base substrate for supporting the carbon nanotube, saidmethod comprising the steps of: forming on the base substrate a baselayer made of an oxidizable base material; forming a porous layer withlarge numbers of pores by causing the base layer to undergo anodicoxidation; forming the carbon nanotube inside the pores; and forming onthe base substrate an anodic oxidation stopping layer for stoppinganodic oxidation of the base substrate, before the base layer undergoesanodic oxidation.
 28. An electron source comprising a field emissionpart which is made up of carbon nanotubes, wherein the carbon nanotubesare structured to partially include an amorphous area.
 29. The electronsource as set forth in claim 28, wherein the field emission part is madeup of solely carbon atoms.
 30. The electron source as set forth in claim28 or 29, wherein an inorganic material is provided between the carbonnanotubes, so as to electrically insulate the carbon nanotubes from oneanother.
 31. The electron source as set forth in claim 30, wherein theinorganic material is an anodic aluminum oxide film.
 32. An electronsource using a carbon nanotube, wherein the carbon nanotube is agraphite that is formed discontinuously by being divided into microareas in a tube axis direction.
 33. The electron source as set forth inclaim 32, wherein the carbon nanotube has a resistivity of 1 kΩ·cm to100 kΩ·cm.
 34. The electron source as set forth in claim 32, comprising:a base substrate, provided with a cathode electrode; a high resistorlayer, which is provided on the cathode electrode; an inorganic thinfilm having pores, provided on the high resistor layer; and the carbonnanotube, which is provided as a field emission part in the pores,wherein a surface of the carbon nanotube in the vicinity of its tip ismodified.
 35. A producing method of an electron source which uses acarbon nanotube, comprising the steps of: forming a cathode electrodewiring on a substrate; forming a high resistor layer on the cathodeelectrode wiring; forming an inorganic material thin film in a fieldemission area on the high resistor layer; forming pores through theinorganic material thin film; disposing the carbon nanotube inside thepores; and modifying a surface of the carbon nanotube.
 36. The method asset forth in claim 35, wherein: the step of forming the pores throughthe inorganic material thin film is carried out after the step offorming the inorganic material thin film in the field emission area onthe high resistor layer, and is carried out by anodic oxidation of theinorganic material thin film, the high resistor layer is an anodicoxidation stopping layer for stopping the anodic oxidation when thepores are formed by anodic oxidation, and the anodic oxidation stoppinglayer is made of at least one kind of material which is selected fromthe group consisting of silicon, silicon carbide, silicon oxide, andsilicon nitride.
 37. The method as set forth in claim 35, wherein themethod of modifying the surface of the carbon nanotube is carried out byetching the carbon nanotube with oxygen plasma.
 38. A producing methodof an electron source which includes a carbon nanotube as a fieldemission part and a support member for supporting the carbon nanotube,said method comprising the steps of: forming the support member with aporous material having large numbers of pores; and depositing carboninside the pores of the porous material in the absence of a metalcatalyst in the pores, so as to form a carbon deposition film of acylindrical shape.
 39. A producing method of a carbon nanotube in whichcarbon is deposited in pores of a porous material having large numbersof pores so as to form a carbon deposition film of a cylindrical shape,said method comprising: an anodic oxidation step for obtaining theporous material; and a heating step of not less than 600° C. after theanodic oxidation step.